Thursday
February 11, 2016

# Posts by Reiny

Total # Posts: 32,937

pre calc
type exponents this way: P(x) = x^3 - 11x^2 + 33x - 35 try values of x = ±1, ±5, ±7 arggh, the last one P(7) worked P(7) = 343 - 11(49) + 33(7) - 35 = 0 so x-7 is a factor after sysnthetic division: P(x) = (x-7)(x^2 - 4x + 5) = 0 x = 7 or by formula, x = (...
October 26, 2015

Algebra
A quick glance at the equations shows that both can be reduced to simpler form 2x + 6y = -12 ---> x + 3y = -6 5x - 5y = 10 ----> x - y = 2 subtract them: 4y = -8 y = -2 sub into x-y=2 x+2 = 2 x = 0 -------- x=0, y=-2
October 26, 2015

Trigonometry
sin 2x/cos 2x = 4 tan 2x = 4 since tan is +, 2x is in either quads I or III 2x = 75.964° or 2x = 180+75.964 = 255.964° x = 37.98° or x = 127.98 since the period of tan 2x is 90° general solution: x = 37.98 + 90k x = 127.98 + 90k since when k=1 we hit 127.98 we ...
October 26, 2015

math
Same type as your previous ones.... ok, I'll do it because of the fractions, but notice the steps are exactly the same slope = (5/4 - 3/2) / (-1/4 - 1/2) = 1/3 so the equation is y = (1/3)x + b sub in your first point (1/2 , 3/2) 3/2 = (1/3)(1/2) + b 3/2 - 1/6 = b b = 4/3 ...
October 26, 2015

Algebra
I see the elements 1,4, and 9 in P Which elements do you NOT see ? in your 2nd question, is that T and K, that is, the intersection of T and K ? if so, which elements can you find that are in both T and K ? If so, then you are correct.
October 26, 2015

Math Geometry
I have to know what topic you are studying now in math, and at what level or grade . Please answer my two previous questions so I can even begin to help you.
October 26, 2015

Math Geometry
To be able to do this question, you MUST be studying parabolas. Have you learned about "completing the square" ? Do you know that for y = ax^2 + bx + c, the x of the vertex is -b/(2a) ? Trying to find out where your difficulties lie.
October 26, 2015

Math Geometry
let the length of the single side by y let each of the other two sides be x so you have y + 2x = 100 , ----> y = 100-2x area = xy = x(100-2x) = -2x^2 + 100x this is a downwards opening parabola. Find the vertex, the x of the vertex is the length of one of the two equal ...
October 26, 2015

math
this is the same kind of question that was answered here, just change the numbers http://www.jiskha.com/display.cgi?id=1445874078
October 26, 2015

Algebra 2
I am sure PsyDAG meant to say y = -11 - 2x and to sub -11-2x or y in the second equation
October 26, 2015

algebra
the factor theorme says that if for some f(x) f(a) = 0 , then x-a is a factor, take it from there tell me what you picked and why
October 26, 2015

math
Since you know the slope is 2, or m=2 so let's start with y = 2x + b we are told that (-1,3) lies on it, so 3 = 2(-1) + b b = 5 equation: y = 2x + 5
October 26, 2015

Math
I don't think it is. My reason is that I substituted your answer in the equation and it did not satisfy. Were you just guessing?
October 26, 2015

algebra
So you want the base of a right-angled triangle, call it x x^2 + 80^2 = 100^2 continue ...
October 26, 2015

math
So the inner dimensions, which determine the volume are: 8-1 or 7 cm 4 cm and 3 cm volume = 7x4x3 cm^3 = 84 cm^3
October 26, 2015

maths
Write down the 7 days of the week. Count the number of days that begin with the letter T. all yours ....
October 26, 2015

maths
Are we talking about the 7 days of the week, with Friday being one of them ? I think I just gave you the answer.
October 26, 2015

Math word problem
you want the absolute value of the difference between the two numbers, that is ... |-11.6 - (-5.43)| =| -6.17 | = 6.17 to understand, place -11.6 and -5.43 on a number line. How far is the distance between you two markings ?
October 26, 2015

Maths
Unless you specify some kind of border, you just have the perimeter of a rectangle with length 30 cm and width 20 cm. Just add up the 4 sides. Make a sketch to help you to visualize the problem.
October 26, 2015

vectors linear algebra
It is easy to find the equation of the L2, since it is parallel to L1 and you have a point on it direction vector of L1 is (-6,2,-4) or reduced: (3, -1, 2) a possible line equation for L2 is x = -3 + 3k y = -3 - k z = -3 + 2k you want x = -12, so -12 = -3 + 3k 3k = -9 k = -3 ...
October 26, 2015

Math
John's age --- x David's present age --- x+3 in 8 yrs: John = x+8 David = x+3 + 8 = x+11 x+8 = (7/8)(x+11) solve for x and finish
October 25, 2015

Math
let's first of all assume that the two 1's are distinguishable, e.g. one is red, the other blue case1, our even number ends in a zero number of such cases = 6x5x4x3x2x1x= 6! = 720 but the two 1's ARE distinguishable, so the number of evens that end in a zero are ...
October 25, 2015

Math- word prolems
let radius be r inches let the height be h inches vol = πr^2h 166.25 = πr^2 h h = 166.25/(πr^2) "economical cylinder" is a function of the surface area, SA SA = 2 circles + rectangles of the side cost = 2(2πr^2) + 6(2πrh) = 4πr^2 + 12&#...
October 25, 2015

math
geeeesh! adding up 5 numbers ??
October 25, 2015

probability
You don't state what the prob of heads or tails are of the biased coin. Just to show the method of my calculations, I will assume the prob(heads) = 3/5 and prob(tails) = 2/5 Make yourself an addition and a multiplication table for 1,2,3,4 In the 16 possible sums, many are ...
October 25, 2015

csc^2 x = 5 or sin^2 x = 1/5 sin x = ± 1/√5 So x is in all 4 quadrants. the reference angle is 26.57° so x = 26.57° x = 180-26.57 = 153.43° x = 180 + 26.57 = 206.57° or x = 360-26.57 = 333.43° just notice that your domain is 0 ≤ x ≤...
October 24, 2015

algebra
let the number be x x-3 = 39-x 2x = 42 x = 21
October 24, 2015

Algebra
I read that as |R-136| ≤ 20 -20 ≤ R-136 ≤ 20 add 136 116 ≤ R ≤ 156 you are correct
October 24, 2015

math
Isaac's law says, T(t) = Ta + (Ts - Ta)e^kt where Ta is the room temp Ts is the temp of the object and t is the time T(6) = 72 + (173-72)e^(6k) 137 = 72 + 101e^6k 101e^6k = 65 e^6k = 65/101 6k = ln(65/101) k = ln(65/101)/6 = -.073455541.. (put in calculator's memory) ...
October 24, 2015

Mathematics
in a GP term(2) = ar = -5 term(5) = ar^3 = 48 ar^3/(ar) = -48/5 r^2 = -9.6 no real solution possible
October 24, 2015

Mathematics
in a GP a = 5 term(3) = ar^2 = 5r^2 = 80 r^2 = 16 r = ± 4 if r = +4 , term(4) = ar^3 = 5(4^3) = 320 if r = -4 , term(4) = ar^3 = 4(-4)^3 = -320 check: if a = 5, r = 4 first 5 terms are: 5, 20, 80, 320, 1280 if a = 5, r = -4 first 5 terms are: 5, -20, 80, -320, 1280 all ...
October 24, 2015

Mathematics
given: a = (1/2)d or d/2 term(8) = a + 7d = d/2 + 7d = 15d/2
October 24, 2015

Calculus help plz
The first part is somewhat vague. Are you finding the derivative of 8(x-y)^12 with respect to x , with respect to y, with respect to ? assuming "with respect to x", d(8(x-y)^12)/dx = 96(x-y)^11 (1 - dy/dx) your second question: y^x + x^y = 17 and x+y=5 Since this ...
October 24, 2015

math
I did the same question about a week ago, all you have to do is change a few numbers. Without doing the actual steps again, watch if near the end, LS = RS , then they do intersect, and you can find the point or LS ≠ RS, then they would NOT intersect
October 24, 2015

simple interest rate
I = PRT 200 = 5000(R)(1) R = 200/5000 = .04 or 4%
October 24, 2015

algebra
.036(57^2) - 2.8(57) = 62.56 = 116.964 - 159.6 + 62.56 = 19.924 , but that is in thousands, so .... 19924 looks like you couldn't read your own writing, look at your first term
October 24, 2015

algebra
Does it sound plausible to you that in an entire country only 65 died in one year ? how did you possible get 65? show me your steps so I can see where you went wrong.
October 24, 2015

algebra
just plug x = 57 into your equation and evaluate. Surely you have a calculator. you probably meant: y=0.036x^2 −2.8x+62.56 , remember to square 57 first, then multiply by .036 Also be mindful that y is per thousand people, so you have to multiply your final answer by ...
October 24, 2015

math
using sum(n) = (n/2)(2a + (n-1)d) and a = 1 sum(20) = 10(2 + 19d) = 20 + 190d sum(40) = 20(2 + 39d) = 40 + 780d sum of next 20 terms = sum(40) - sum(20) = 40+780d - 20 - 190d = 20 + 590d 20+190d = (1/3)(20+590d) 60 + 570d = 20+590d 40 = 20d d= 2 sum(30) = 15(2 + 29d) = 30 + ...
October 24, 2015

Calculus 1
Already factored, nice So all we have to do is set each factor equal to zero x^(4/5) = 0 ----> x = 0 , f(0) = 0 (x-1)^2 = 0 ----> x = 1 , f(1) = 0 F ' (x) = x^(4/5) (2(x-1)) + (4/5)x^(-1/5) (x-1)^2 = (2/5)x^(-1/5) (x-1) [5x + 2(x-1)] = (2/5)(x-1)(7x-2)/x^(1/5 = 0 for...
October 23, 2015

maths
unit digit --- x ten's digit ---- 4x clearly obvious that x can only be 1 or 2 So the number could be only 41 or 82 and the number with the digits reversed of those is 14 and 28 which has a difference of 54 ?
October 23, 2015

maths
daughter's share = 1 - 1/2 - 1/3 = 1/6 (1/6)x = 5000 x = 30000 take over
October 23, 2015

Algebra
Now you have changed the question from your previous post. If all you know is the perimeter to be 172, the answer would not be unique e.g. suppose the rectangle is 50 and 36 ft (notice perimeter is 172) area = 50(36) or 1800 ft^2, thus we need 1800 tiles e.g. suppose the ...
October 23, 2015

Algebra
No, you are filling the rectangle with the tiles, so we are talking about AREA. area = 60 x 26 = 1560 so you need 1560 tiles (the fact that the perimeter is 172 ft was not needed, we could have calculated that anyway)
October 23, 2015

algebra
you are just finding the hypotenuse of a right-angled triangle with sides l and 7l Hyp^2 = l^2 + (7l)^2 = 50l^2 hyp = √(50l^2) = 5√2 l
October 23, 2015

MATH
solve for x (1/2)x - 9 = 14 you should be able to solve this equation in your head.
October 22, 2015

Did you make a sketch? If so, it should be intuitively obvious that the angle must be 60°, since the resultant will form an equilateral triangle with the two given vectors
October 22, 2015

Math
rate of reading at the beginning = 40 pages/hr at that rate the time to read 150 pages = 150/40 hrs or 15/4 hours Time left to read the other 250 pages = 6-15/4 or 9/4 hrs rate of reading needed to finish the book = 250/(9/4) = 111 1/9 pages per hour or appr 1.85 pages per minute
October 22, 2015

Math
f(x) = 4√(√x + 6) = 4(2 x^(1/2) + 6)^(1/2) f ' (x) = 2(2x^(1/2) + 6)^(-1/2) (x^(-1/2) ) = 2/(√x(2√x + 6) )
October 22, 2015

algebra
for a reflection over the x-axis, the x's stay the same, but the y's change to their opposites. I will do point B B(3,-2) ----> B' (3,2) you do the rest. I suggest to make a sketch to confirm what you did
October 22, 2015

algebra
Tricky question . Are we dealing with a parabola? I will assume we are. Since the axis of symmetry is neither horizontal nor vertical, we got a mess. Before I start, I want to make sure you did not have a typo. Let me know.
October 22, 2015

Albegra
number of adult tickets ---- x number of children's tickets ---- 325-x solve for x ..... 3.5x + 2(325-x) = 875
October 22, 2015

Algebra
number of dimes --- x number of quarters = x+3 number of nickels = x-5 solve for x x + x+3 + x-5 = 52
October 22, 2015

Math
The best webpage for this kind of problem on the entire internet Just enter you data http://davidmlane.com/hyperstat/z_table.html
October 22, 2015

MATH
amount given by Maya to Emily --- x after the give-away: Maya ---- 2740 - x Emily ---- 3560 + x 3560 + x = 4(2740 - x) take over
October 22, 2015

math
Let's hope they are on separate tracks. let distance covered by faster train be x miles then distance covered by slower train is 800-x When they pass each other, their times must be the same, so ... x/67 = (800-x)/53 53x = 53600 - 67x 120x = 53600 x = 446 2/3 miles time = ...
October 22, 2015

mathematical statistic
2 initial cases: case 1, the ball drawn from urn A to B is W urn B now has 8W and 5B prob (W and W) = prob(W from A AND W from B) = (6/9)(8/13) = 48/117 rest of problem to check my answer: prob(W and B) = (6/9)(5/13) = 30/117 case2: the ball from urn A to urn B is B Prob(B and...
October 22, 2015

Calculus
let the width of the photo be x in then the length of the photo is 128/x in width of poster = x+8 length of poster = 128/x + 8 Area = (x+8)(128/x + 8) = 128 + 8x + 1024/x + 64 d(area) = 8 - 1024/x^2 = 0 for a min of area 8 = 1024/x 8x^2 = 1024 x^2 =128 x = √128 = 8√...
October 21, 2015

Math (Trig)
distance in the direction of the bearing = 6(15) or 90 n miles. make your sketch to see: sin 25° = x/90 x = 90sin25 = appr 38.04 n miles cos25= y/90 y = 90cos25= 81.57 n miles
October 21, 2015

Math
according to your explanation, #1 is 120 ≤ (135+145+n)/3 ≤ 145 120 ≤ (280 + n)/3 ≤ 145 times 3 360 ≤ 280 + n ≤ 435 subtract 280 80 ≤ n ≤ 155 do the others the same way
October 21, 2015

Math
so we have (-1 + i√3)^12 let u = -1 + i√3 = √10(cos(2π/3) + i sin(2π/3)) u^12 = √10^12(cos 8π + i sin 8π) = 10^6( 1 + i(0)) = 10^6 or 1,000,000
October 21, 2015

Math
1 D is correct For #2, you answer of B wouldn't do anything to the point, that is what you started with reflections in the x-axis leave the x alone but change the y to the opposite, so (6,-2) ---< (6,2)
October 21, 2015

math
work the problem in one set of units, e.g. cm All your really need to know : 1 inch = 2.54 cm Annalisa = 64 inches = 162.56 cm Stefan is 7.5 cm taller , so Stefan = 170.06 cm Keiko is 1.5 inches or 3.81 cm shorter than Stefan Keiko = 166.25 To convert to inches, just divide ...
October 19, 2015

math
umhhh, why not look back at your earlier posts before reposting the same question ? http://www.jiskha.com/display.cgi?id=1445204064
October 18, 2015

math
for L1, direction vector is (3,-1,-1) and an equation is x = 1 + 3t y = -t z = -1 - t for L2, a possible equation is x = -6 - 3k y = 21 + 9k z = -8 - 3k if they intersect, 1+3t = -6-3k AND -t = 21+9k AND -1-t = -8-3k using the first two equations, 1 + 3(-21-9k) = -6-3k -62 - ...
October 18, 2015

Complete the Square
The hardest type have fractional coefficients that are relatively prime. I will give you one, and solve it, you pick 4 more like it y = (2/3)x^2 + (5/7)x - 11/13 factor the coefficient (divide it out) of the x^2 terms from the first two terms, leave the constant term trailing ...
October 18, 2015

algebra
I tried factors of 6 and found f(-2)=0 and f(3) =0 so after successive synthetic divisions I had the factors, (x+2)(x-3)(7x^2 - 2x - 1) solving (x+2)(x-3)(7x^2 - 2x - 1) = 0 x = -2, 3, or (2 ±√32)/14 = -2, 3, or (1 ± 2√2)/7
October 17, 2015

Math (help)
f(1) = 0 , after the first try so x-1 is one of the factors, by synthetic division we have (x-1)(2x^3 + x^2 + 8x + 4) , notice we can group the last one =(x-1)( x^2(2x+1) + 4(2x+1) ) = (x-1)(2x+1)(x^2 + 4) = 0 for zeros of the function, so x = 1 , -1/2 , or ±2i
October 17, 2015

St Eugene university
First of all: St Eugene university is not a school subject second: I can't make any sense out of your post. Is it: x^2 * (second derivative of -3x) * (first derivative of -5y) = sin(logx) ?? is it the derivative with respect to x ? then 2nd derivative of -3x is 0, and you ...
October 17, 2015

Luhlaza high school
a = 2 v = 2t + c , where c is a constant and t is in seconds when t = 0 , v = 0 0 = 0(t) + c ----> c = 0 so v = 2t after 10 s, v = 2(10) or 20 m/s
October 17, 2015

Math
William's age --- x Jon's age ------ x+6 in 2002: x+6 = 4(x-5) + 2 x+6 = 4x - 20 + 2 -3x = -24 x = 8 so william is 8 in 2002 and Jon is 14 in 2002 you do the rest
October 17, 2015

Probability
prob(rotten) = 2/2 = 1/6 prob(not rotten) = 5/6 You want prob that none of 4 are rotten = C(4,0)(1/6)^0 (5/6)^4 = 1(1)(625/1296) = 625/1296
October 16, 2015

math
Quite easy .... Make a sketch, draw in the altitude, and mark the centre. The radius is 12 cm, and the distance from the centre to the triangle must then be 6 cm You have a right-angled triangle with one leg 6, the hypotenuse as 12 and a missing base, call it x x^2 + 6^2 =12^2...
October 16, 2015

Calculus
let each side of the square that you cut out be x " Recall that volume of a box = length x width x height Make a sketch showing the cut-outs, you will see that length = 32-2w width = 24-2w height = w V = w(32-2w)(24-2w) = 768w - 112w^2 + 4w^3 dV/dw = 768 - 224w + 12w^2 = ...
October 16, 2015

math
amount at end of 3 years = 4000+960 = ... I = PRT 960 = 4000(R)(3) R = 960/12000 = .08 or 8% had the interest been 9% I = 4000(.09)(3) = 1080 take over
October 16, 2015

Maths
I am sure you meant 6% each year, not each day (at per day, the answer would be an absurdly large number) after 1 year -- 20000(1.06) after 2 years -- 20000(1.06)^2 .. after 8 years: amount = 20000(1.06)^8 = ....
October 16, 2015

math
Make a sketch Clearly the ship with the smaller angle is farther away. Label the two ships A and B, B closer to the lighthouse. Label the top and bottom of the lighthouse P and Q. enter the angles and AB=200 in triangle ABP, I have angle A = 30° angle ABP = 135° angle ...
October 16, 2015

count the days Interest = 720(.07)(days/365) =
October 16, 2015

maths
proof of what Justin said: let sides of original square be x by x perimeter = 4x new length = x+3 new width = x-3 new perimeter = 2(x+3) + 2(x-3) = 2x + 6 + 2x - 6 = 4x , just as before so original side = 84/4 = 21
October 16, 2015

maths
now: width --- x length -- x+7 after change: width = x-3 length = x+7 - 10 = x-3 (notice the new rectangle is now a square) original area = x(x+7) new area = (x-3)(x-3) the difference is 95 , so .... x(x+7) - (x-3)^2 = 95 x^2 + 7x - (x^2 - 6x + 9) = 95 carry on, it is easy
October 16, 2015

Algebra
amount at 6% ---- x amount at 7% --- 29000-x solve for x .06x + .07(29000-x) = 1895
October 16, 2015

math
4sinØ = -1, 0° ≤ Ø ≤ 360° sinØ = -1/4 my calculator gives me Ø = -14.48° but that is outside our domain Here is how I do those types: Since sinØ is negative, I know that my angle Ø must be in quadrants III or IV...
October 16, 2015

Algebra
Plug it in y = -2x -4 = -2(1) -4 = -2 is that a true statement? If it is, then your point is a solution, otherwise ....
October 16, 2015

math
I should have pointed out that there are two types of deviation. One is called Population Standard Deviation, where you divide by n, the number of data values The other is the Standard Deviation, where you divide by n-1 , where n is the number of data values. You can see ...
October 16, 2015

math
https://www.easycalculation.com/statistics/standard-deviation.php
October 16, 2015

Algebra
#4 but you typed 2/8, not 2/9 that is why both me and Bob labeled it incorrect. yes, the correct answer is 2/9 #3 so we have 3/4 wall in 1 hour or 3/4 wall in 60 minutes thus (3/4)÷60 or 1/80 of a wall in 1 minute
October 16, 2015

Algebra
#3 probably contains a typo, and it must have asked for the rate per hour, not per minute She did paint 3/4 of the wall in 1 HOUR. #4, check your calculation, you are close. You did multiply your quotient answer by 2 ??
October 16, 2015

Trig
length --- x width = x+9 height = x-1 volume = x(x-1)(x+9) This is not trig.
October 15, 2015

Math(HELP!)
let the length parallel to the barn be y ft let the two other sides be x ft each so 2x + y = 120 y = 120 - 2x area = xy = x(120-2x) = -2x^2 + 120x this is a downward parabola, the x of the vertex is -b/2a = -120/-4 = 30 then y = 120-60 = 60 So the largest area is 30(60) or ...
October 15, 2015

algebra
and ??
October 15, 2015

Pre-Calculus
An hour?? Did you make a sketch? Mine is a right-angled triangle with base angle of 40°, a horizontal of x, and a vertical of 75 ft, and a hypotenuse of h "How far out is the ship from the lighthouse" is a vague question. Do you want the direct distance between ...
October 15, 2015

Math
in the simplification process you would have to state it this way .... y=(x^2+x-12)/(x+4) = (x-3)(x+4)/(x+4) = x - 3 , x ≠ -4 So in effect y=(x^2+x-12)/(x+4) is the same as y = x - 3 for every value of x except -4 If we sub x = -4 into y = x-3, we get y = -7 If we sub x...
October 15, 2015

algebra 1
Did you translate the English into Math ? "nine tenths of a number g" ---> (9/10)g "is the same as" ----> = "seven plus two thirds of another number k " ---> 7 + (2/3)k follow the same steps I showed you many posts ago let me know what ...
October 15, 2015

algebra 1
not possible t - 7 = t -7 = 0 ----> contradiction
October 15, 2015

HELPPP
Really ?? http://www.jiskha.com/display.cgi?id=1444950413 http://www.jiskha.com/display.cgi?id=1444950445 http://www.jiskha.com/display.cgi?id=1444951131
October 15, 2015

algebra 1
follow my method I showed you in the previous ones I did for you. Show me your work
October 15, 2015

algebra 1
Why are you having difficulties with these? They all seem like the same type. (df + 10)/6 = g times 6 df + 10 = 6g subtracct 6 df = 6g - 10 divide both sides by d f = (6g-10)/d OR 6g/d - 10/d
October 15, 2015

algebra 1
10m = p - N m = (p - N)/10
October 15, 2015

Pre-Calc
Just translate the English into Math Ming's age --- x Jeffs age is 3x Tina's age = 2x+4 next year: Jeff's age = 3x+1 Ming's age = x+1 It said: 3x+1 = 2(x+1) + 7 3x+1 = 2x+2+7 x = 10 So today: Ming is 10 Jeff is 30 Tina is 24 A. So it looks like today, Tina is 2...
October 15, 2015