Friday
November 28, 2014

Posts by Reiny


Total # Posts: 27,978

Math
by Pythagoras, you can find MW = 12 then cosW = 12/13
November 9, 2014

college algebra
same post
November 9, 2014

college algebra
x^4 +12x^3 +10x^2-9x+9x+22=0 I suspect a typo, why would you have two x terms without combining them?
November 9, 2014

calculus
y' = (4x+3)^5 (-4)(5x+2)^-5 (5) + (5x+2)^-4 (5)(4x+3)^4 (5) = -20(4x+3)^5 (5x+2)^-5 + 20(4x+3)^4 (5x+2)^-4 take it further if there is need by taking out a common factor of 20(4x+3)^4 (5x+2)^-5
November 9, 2014

Math - Word problem
Mary, your problem is a variation of the famous "spider and fly" problem. Here is a webpage that has the same concept, you have an electrical outlet and box instead of spider and fly. http://mathworld.wolfram.com/SpiderandFlyProblem.html Use Steve's instructions ...
November 9, 2014

Algebra 2
you just proved my point, you forgot to switch back to one of your other names
November 9, 2014

Algebra 2
Don't change names, stick to one name follow the same steps I showed you yesterday for the same type of problem http://www.jiskha.com/display.cgi?id=1415491412 expand first, then bring everybody to the left and factor. Remember the right side has to be zero.
November 9, 2014

Algebra 2
follow the same steps I showed you yesterday for the same type of problem http://www.jiskha.com/display.cgi?id=1415491412 expand first, then bring everybody to the left and factor. Remember the right side has to be zero.
November 9, 2014

calculus
follow the steps I just showed you for your previous problem (same thing)
November 9, 2014

calculus
f(f(x)) = f(4x^2 - 1) = 4(x^2 - 1)^2 - 1 don't know if you have to expand that, leave that up to you g(f(x)) = g(4x^2 - 1) = 4/(4x^2 - 1)
November 9, 2014

average
Reverse your thinking. How do you think they found the average of those 4 numbers to be 36 ?
November 9, 2014

Calc
notice the point (4,0) does not lie ON the curve. So your sketch should show that. let that point be (a,b) so we know b = √a or a = b^2 dy/dx = (1/2)x^(-1/2) or 1/(2√x) so at the point (a,b) the slope of the tangent is 1/(2√a) I will use the property that at ...
November 9, 2014

math
number of men --- m number of women --- w number of children --- c m+w+c = 180 , #1 m = 2w , #2 w = 3c , #3 from #2 , w = m/2 then in #3, 3c = w c = (1/3)w = (1/3)(m/2) = m/6 back in #1 m+w+c = 180 m + m/2 + m/6 = 180 times 6 6m + 3m + m = 1080 10m= 1080 m = 108 then w = m/2...
November 9, 2014

Calc
why not just state the equation of the parabola, then we can do the question
November 9, 2014

Algebra
you want g(x) = g(x) , so x^3 + x^2 + x - 1 = x^3 - x^2 + x + 1 2x^2 = 2 x^2 = 1 x = ± 1 if x = 1 , g(1) = 1 - 1 + 1 + 1 = 2 if x = -1 , g(-1) = -1 - 1 - 1 + 1 = -2 so they intersect at (1,2) and (-1,-2)
November 9, 2014

Algebra
Are we to assume that your line AB is a straight line? If so, we can find the slope of AB slope AB = (b^2 -a^2)/(b-a) = (b-a)(b+a)/(b-a) = b+a we can write the equation as y - a^2 = (b+a)(x-a) also (3/2,0) lies on it, so 0-a^2 = (b+a)(-3/2 - a) -a^2 = -3b/2 -ab - 3a/2 - a^2 3b...
November 9, 2014

maths
I made a sketch and it looks like a simple cosine law problem d^2 = 10^2 + 3^2 - 2(10)(3)cos135 = 151.426... d = 12.3 km/hr then to find the small acute angle Ø sinØ/3 = sin 135°/12.3.. sinØ = .1723.. Ø = 9.927° direction is S (45-9.927..)&...
November 9, 2014

Trigonometry
if you want the direct line distance (along the hypotenuse) sin 19.5 = 939/d d = 939/sin19.5 = 2813 m If you want the horizontal displacement tan 19.5 = 939/x x = 939/tan19.5 = 2652 m to the nearest metre
November 8, 2014

Algebra 2
x^2 - 13x +40 = x x^2 - 14x + 40 = 0 (x-10)(x-4) = 0 x = 10 or x = 4
November 8, 2014

Algebra 2
expand it first 4x^2 - 24x - x^2 + 2x + 24 = 0 3x^2 - 22x + 24 = 0 (x-6)(3x - 4) = 0 x = 6 or x = 4/3
November 8, 2014

Algebra 2
probably the most method used for 3by3 equations is called elimination The object is to eliminate one or more variables from pairs of equations. Usually we look at the coefficents of each variable and choose the one with the smallest or simplest numbers. In this case it doesn...
November 8, 2014

Trigonometry
No idea where A , B , or C are
November 8, 2014

arithmetic
First of all, you are using the formula for a geometric, yours is an arithmetic Secondly, the sentence "the 20th sum of an arithmetic progression is -7 and the sum of the first 20 terms is 620" makes no sense to me what does "the 20th sum" mean ?
November 8, 2014

Trigonometry
diagrams don't show up in this format You will have to give a good description
November 8, 2014

math
yes, that is one of the rules of powers e.g (2x3)^4 = (2^4)(3^4) =(16)(81) =1296 or (2x3)^4 = 6^4 = 1296
November 8, 2014

math
a) two cases: bw or wb case 1: first ball is b, prob(b) = 7/12 so 3 black balls are added, now we have 5 w, 10 b prob(w) = 5/15 = 1/3 prob(case1) = (7/12)(1/3) = 7/36 case 2: first ball is w, prob(w) = 5/12 so 3 white balls are added, now we have 8w, 7b prob(b) = 7/15 prob(...
November 8, 2014

math
How can you get a sum of 10 on 2 dice ? only ways: 4,6 6,4 5,5 and there are 36 ways for the 2 dice to fall, so prob(sum of 10) = 3/36 = 1/12 btw "throne" ---> thrown
November 8, 2014

Intermediate Algebra
amount at 6% === x amount at 14% ---- 17000-x solve for x .06x + .14(17000-x) = 1500 I would multiply each of the 3 terms by 100 to get rid of the decimals 6x + 14(17000-x) = 150000 etc
November 8, 2014

equation
a is 30% of b --- > a = 3/10b 3b = 10a b = 10a/3 = (10/3)a = 3.3333..a = 333 1/3 % a
November 7, 2014

AP CALC. AB
a) let the height of the sand in the box be h inches V= (40)(20)(h) = 800h dV/dt = 800 dh/dt -300 = 800dh/dt dh/dt = -300/800 = -3/8 inches per minute b) part 2 V = (1/3)π r^2 h dV/dt = (13)π r^2 dh/dt + (2/3)π r h dr/dt plugging in our information ... 300 = (1/...
November 7, 2014

math again (last question help!!!)
first one --x 2nd one -- y 3rd one -- 35-x-y x+y = 20 y + (35-x-y) = 28 --- > x = 7 (then 7+y =20 ---> y = 13 35-x-y = 35-7-13 = 15 first shelf has 7 2nd shelf has 13 third has 15 check: 1st plus 2nd = 7+13 = 20 , check! 2nd plus 3rd = 13+15 = 28, check! all is good
November 7, 2014

Math
x(1.0225)^30 = 50000 solve for x to get x = 25649.00
November 7, 2014

Math Trig Please Help!!!
Make a real effort to memorize the trig ratios for these basic right-angled triangles 45-45-90 degree triangle ---> 1 -- 1 -- √2 30-60-90 degree triangle ---> 1 -- √3 -- 2 make a quick sketch of these triangles, It is easy to see where the values go. Remember...
November 7, 2014

Math
sin^-1 .5 = .5236 radians sin(.5^-1) = sin(2) = .909297 (sin .5)^-1 = .47942..^-1 = 2.08583
November 7, 2014

Math Help!
treat (2Ø+8) as you angle then, do tan^-1 (.489) = x x = .45481 radians but the tangent was negative so 2Ø+8 = π-.45481 2Ø = -5.313216.. Ø = -2.65661 or 2Ø+8 = 2π-.45481 Ø =-1.0858.. as you can see those two answers are ...
November 7, 2014

Math Trig Help
recall that sinØ = opposite/hypotenuse = x/3 so you have a right angled triangle with opposite = x and hypotenuse = 3 let the adjacent be a a^2 + x^2 = 3^2 a^2 = 9 - x^2 a = ± √(x^2 - 9) , but Ø is in I, so a = √(x^2 - 9) cosØ = √(...
November 7, 2014

Math
sinØ = 1/4, so opposite = 1, hypotenuse = 4 by Pythagoras, adjacent = √15 secØ = 1/cosØ = 1/(√15/4) = 4/√15 tan Ø = 1/√15
November 7, 2014

Math
sec 7pi/4 = 1/cos(7π/4) 7π/4 is in quad IV, where the cosine is positive 7π/4 is π/4 away from the x-axis so cos7π/4) = 1/√2 so sec 7π/4 = √2
November 7, 2014

Math
here is my answer from 2 years ago http://www.jiskha.com/display.cgi?id=1351706906 there are other answers in the "Related Questions" below
November 7, 2014

Math
use the same webpage I just gave you for c) , enter y = x^3
November 7, 2014

Math
play with with by editing the equation in the subject box http://www.wolframalpha.com/input/?i=y+%3D+%7Cx-2%7C
November 7, 2014

Math Question
slope = (4-(-2))/(-2-3) = -6/5 y+2 = (-6/5)(x-3) 5y+10 = -6x + 18 6x + 5y - 8 = 0 or 6x + 5y = 8 or y = (-6/5)x + 8/5
November 7, 2014

algebra and geometry
if 1 inch ---> 4 ft then 2 inches by 5 inches ---> 8 ft by 20 ft
November 7, 2014

math
Looks like a simple case of Pythagoras d^2 = 15^2 + 8^2 = 289 d = √289 = 17 m
November 7, 2014

math
You will have to know to how many decimal places you want to round. best shown with an example 12.3567 suppose you are asked to round to 3 decimal places. Look at the 4th decimal place. If that is from 0 to 4, the digit in the 3rd decimal stays the same. If the 4th decimal is ...
November 7, 2014

mathematics
volume of cylinder is area of base x height since you are given both of these, just sub in and do the arithmetic.
November 7, 2014

math
present: Mario's age --- x Bert's age ----- 2x+5 Nine years ago: Mario --- x-9 Bert ---- (2x+5) - 9 = 2x -4 "Nine years ago, the sum of their ages is 50. " ----> x-9 + 2x-4 = 50 3x = 63 x = 21 Mario is now 21 and Bert is now 47 check: 9 yrs ago Mario was ...
November 7, 2014

Calculus
from xy^2 = 16 y^2 = 16/x now sub that into F = x^2 + y^2 = x^2 + 16/x dF/dx = 2x - 16/x^2 = 0 for max/min 2x - 16/x^2 = 0 2x = 16/x^2 2x^3 = 16 x^3 = 8 x = cuberoot(8) = 2 if x = 2 , y^2 = 16/2 = 8 ---> y = ±√8 or ±2√2 then F = x^2 + y^2 = 4 + 8...
November 6, 2014

Intermediate Algebra
why did you switch signs ??? x3 – 380x2 + 2x – 760 = 0 x^2(x - 380) + 2(x - 380) = 0 (x - 380)(x^2 + 2) = 0 x = 380 or x^2 = -2 , the latter has x not a real number so x = + 380
November 6, 2014

Algebra/Math
f(x) = 3x + b f^-1 (x) = (x - b)/3 (-3, a) lies on both so f(-3) = -9 + b = a f^-1(-3) = (-3-b)/3 = a (-3-b)/3 = -9+b -3-b = -27 + 3b 24 = 4b b = 6 then a = -9+6 = -3 a = -3, b = 6 check my arithmetic
November 6, 2014

Calculus-Newton Method Approximation
1/ 3(x^3) + 1/2(x^2) + 1 = 0 times 6 2x^3 + 3x^2 + 6 = 0 let y = 2x^3 + 3x^2 + 6 dy/dx = 6x^2 + 6x according to Newton's method newx = x - y/y' = x - (2x^3 + 3x^2 + 6 )/(6x^2 + 6x) = (6x^3 + 6x^2 - 2x^3 - 3x^2 - 6)/(6x^2 + 6x) = (4x^3 + 3x^2 - 6)/(6x^2 + 6x) using my ...
November 6, 2014

Math/Algebra
let's find their intersection points 1+x^2+x^3 = 3-x^2+x^3 2x^2 = 2 x^2 = 1 x = ± 1 if x = 1, y =1+2+1 = 3 if x = -1, y = 1 + 1 - 1 = 1 They intersect at (1,3) and (1,1) so what is the difference between their y values ?
November 6, 2014

Algebra
√((x-2)^2 + (y-7)^2 = 13 square both sides and expand x^2 - 4x + 4 + y^2 - 14y + 49 = 169 x^2 - 4x + y^2 - 14y = 116 but x = 10+2y sub that into the first equation (10+2y)^2 - 4(10+2y) + y^2 - 14y = 116 100 + 40y + 4y^2 - 40 -8y + y^2 - 14y = 116 5y^2 + 18y - 56 =0 (y-2...
November 6, 2014

Math
So we are going to need those intercepts, the x - intercepts are easy x = 3 or x = -2 for the y-intercept, let x = 0 y = (-3)^2 (2) = 18 so the points of the triangle are (3,0), (-2,0) and (0,18) so the base of the triangle is 5 and the height is 18 area = (1/2)(base)(height...
November 6, 2014

statistic
a) prob(red) = .546 prob(not red) = .454 prob(exactly 5red) = C(12,5) (.546)^5 (.454)^7 = appr .153 b) prob (green) = .395 prob(not green) = .605 prob(at least 3 green) = prob(3green) + prob(4 green) + ... + prob(12 green) =1 - prob(0 not green) - prob(1 not green) - prob(2 ...
November 6, 2014

math
c is wrong 3^3 = 27 , so 27 is a perfect cube.
November 6, 2014

geometry
what is 8/9 yards ?
November 6, 2014

Math
I suspect you meant: c(t) = 9 - 90 000 (1/ (10 000 + 3t) ) I will also assume that c(t) is in kg/m^3 then 6 = 9 - 90 000 (1/ (10 000 + 3t)) 90000(1/(10000+3t)) = 3 30000 + 9t = 90000 9t = 60000 t = 6666 2/3 minutes ? check my arithmetic
November 6, 2014

Trigonometry
Did you make your sketch? Mine is triangle ABC with angle A = 55° angle C = 22°, and angle B + 103° then it is just a matter of the sine law: AC/sin103 = 300/sin22 I got AC = appr 780 miles
November 6, 2014

geometry
There would be an infinite number of such triangles. What part of the instructions are you having difficulties with ?
November 6, 2014

Maths
make your sketch draw a horizontal line from the top of the shorter pole to the other pole. You now have a right-angled triangle with base 12 m, height 18-13 or 5 m You should recognize the common 5,12, 13 right-angled triangle, if not c^2 = 12^2 + 5^2 = 169 c =√169 = 13
November 5, 2014

Algebra
adults --- x children -- y seniors --- z x+y+z = 895 , #1 14x +11y + 8z = 10514 , #2 translation of: "If the combined number of children and adult tickets exceeded twice the number of senior citizen tickets by 295" ---> x+y > 2z by 295 x+y = 2z + 295 x + y - 2z...
November 5, 2014

Trig
"A playground slide starts 107cm above the ground and is 250cm long" Trusting my English grammar somewhat, you made "slide" the subject of your sentence, and you said it is 250 cm long. Thus 250 is the hypotenuse. tanØ = opposite/adjacent sinØ...
November 5, 2014

Trig
Assuming the slide is a straight line, (most are not) Did you make your sketch? I have the opposite as 107 and the hypotenuse as 250 so sinØ = 107/250 Ø = appr 25°
November 5, 2014

please help, math question
let the width of the matte be x all around so the width of the whole picture = 10+2x and the length is 15+2x area of whole picture = (10+2x)(15+2x) area of picture = 10(15) = 150 area of matte only = (10+2x)(15+2x) - 150 so (10+2x)(15+2x) - 150 = 150 150 + 20x + 30x + 4x^2 - ...
November 5, 2014

Algebra 2
let x be the larger then the smaller is 96-x x - (96-x) = 17 x - 96 + x = 17 2x = 113 x = 56.5 larger is 56.5 , the smaller is 39.5 check: difference = 56.5-39.5 = 17 , yup!!
November 5, 2014

Vertex, Focus, & Directrix of Parabolas
Just did this for Kayla http://www.jiskha.com/display.cgi?id=1415240099
November 5, 2014

Math
x( 1 - 1.02^-11)/.02 = 1700 x( 9.786848.. = 1700 x = $ 173.70
November 5, 2014

Algebra II
writing it in terms of y first of all 48y = x^2 - 12x + 276 or 48y = x^2 -12x + 36 - 36 + 276 48y = (x - 6)^2 + 240 y = (1/48) (x-6)^2 + 5 so the vertex is (6,5) the x of the focus is the same as that for the vertex so x = 6 for y = (1/48)x^2 - (1/4)x + 23/4 the y of the focus...
November 5, 2014

Math HELP!
What did we do to the 7 to make it a 2 ? looks like we subtracted 5 What did we do to the -3 to turn it into a 5 ??? so (x,y) ---> (x-5, ..........) I am sure you can get this
November 5, 2014

math
I did this same problem 2 years ago http://www.jiskha.com/display.cgi?id=1352760453 Looks like this teacher is just recycling the same problems
November 5, 2014

Math
for any parabola of the form y = a(x-h)^2 + k , the vertex is (h,k) and the axis of symmetry is x = h so in your case ......
November 5, 2014

math
it should not be too hard to actually list them Q-D-N 0 0 6 0 1 4 0 2 2 0 3 0 1 0 5
November 5, 2014

Finance
what is 1000(1.07)^20 ?
November 5, 2014

trigo
distance covered by both wheels must be the same ... with radians, arclength is simply rØ so 24Ø = 60(12) Ø = 30 radians
November 5, 2014

Algebra
Don't know what you want to "solve" You have a cubic function, are you graphing it? are you finding intercepts? ??
November 5, 2014

Probability
prob(right) = 1/4 prob(wrong) = 3/4 if passing grade is 8/10, then I will pass if I get 8/10 or 9/10 or 10/10 prob of that = C(10,8)(1/4)^8 (3/4)^2 + C(10,9)(1/4)^9 (3/4) + (1/4)^10 = appr .00041 check my arithmetic
November 5, 2014

college statistics
C(12,3) = 12!/(3!9!) = 220 Added attraction: Google Pascal's triangle look at the row: 1 12 66 220 495 .... here is a good one.. http://ptri1.tripod.com/
November 5, 2014

algebra
Your answers make no sense to me. How did you get these?
November 4, 2014

algera
find the derivative, set it equal to zero and solve.
November 4, 2014

algebra
You left your answer choices blank. What did you get?
November 4, 2014

Calculus
BUT, the given point is not on the curve, so what you did is bogus. look at your sketch, the point (0,-4) is below the parabola. Draw the two tangents, you will see that it touches the curve at two different points, one in the first quad, the other in the 2nd quad. Let the ...
November 4, 2014

Calculus
y' = 18x^2 + 5 we want 18x^2 + 5 = 4 18x^2 = -1 x^2 = -1/18 but that is not possible since the square of anything has to be positive, so there is value of x making this equations true thus there is not slope of 4 thuse there is no such tangent
November 4, 2014

Calculus
dy/dx = 6x^2 - 6x - 6 = 0 for a horizontal slope x^2 - x - 1 = 0 x = (1 ± √5)/2 = appr 1.618 or -.618 you are correct, but all it asked for is the values of x (did you know that the first answer x = 1.618.. is the "golden ratio " ? )
November 4, 2014

Calculus
correct
November 4, 2014

math
look at one of the 6 congruent triangles the base of it must be 78/6 = 13 area of one of them = (1/2)base x height = (1/2)(13)(11) = 143/2 square inches so the whole hexagon is 6(143/2) = 429 inches^2
November 4, 2014

math
adults --- x children --- 3x 7x + 3(3x) = 6000 16x = 6000 x = 375 so 375 adults and 1125 kids for a total of 1500 sold
November 4, 2014

Math
cost per quart for orange --- x cost per quart for grapejuice -- x-1 (5/2)(x-1) + (3/2)x = 12.5 times 2 5(x-1) + 3x = 25 8x = 30 x = 3.75 x-1 = 2.75 orange juice costs $3.75 per quart and grape juice costs $2.75 per quart
November 4, 2014

math
I am 100% sure it was measured in feet. Looks like Sandy is a kid or a short junior. The stick should come to your chin with skates on, and to about your nose without skates on.
November 4, 2014

algebra
number of dimes --- x number of nickels --- 2x 10x + 5(2x) = 120 20x = 120 x = 6 So 6 dimes and 12 nickels
November 4, 2014

Algebra
I have a feeling you meant f(x) = (x+5)/3 or is it the way you typed it ? confirm please
November 4, 2014

math
looks like plain ol' Pythagoras to me y^2 + 2.8^2 = 10.5^2 y^2 = 102.41 y = √102.41 = appr 10.12 m
November 4, 2014

Algebra please help
since a 2 ounce bag is 1/3 of a 6 ounce bag, I predict it will cost one third of $3.60.
November 4, 2014

Algebra please help answer
clearly 9:6 ≠ 4:3
November 4, 2014

algebra
I am assuming that the 2nd shift follows the first shift now: let the number of girls in A be x let the number of girls in B be y after 1st shift: A has x-7 B has y+7 "the number of girls in the classes would interchange" ---> y+7 = x 2nd shift A has x-7 + 4 = x-3...
November 4, 2014

Algebra
Are you sure you don't have any more information, such as an angle ? otherwise, let the third side be y P = 2(3x+2) + y
November 3, 2014

Math: permutation
let's choose the consonants and vowels first No of combinations = C(5,2) x C(2,1) = 10(2) = 20 Since you titled your post "permutations" we now want to arrange these. That can be done in 6 ways each So the number of permutations is 6(20) = 120
November 3, 2014

Math
looks like you are studying the binomial theorem You MUST memorize some basic formulas e.g. for (a+b)^n term(r+1) = C(n,r) (a^r)(b^(n-r)) so for (3x+9)^9 term6 = C(9,5)(3x)^5 y^4 = 126(243x^5)y^4 = 30618 x^5 y^4 b) what is the middle term for (3x + y^3)^8 ? c) let that term be...
November 2, 2014

Math
2.25 = 1(10^8) 1.5^(t/20) since the time would be same for a small country or a large country to increase by 124%, we can ignore the 10^8 take log of both sides log 2.25 = l log 1.5^(t/20 log 2.25 = (t/20) log 1.5 log2.25/log 1.5 = t/20 t = 20(log2.25)/log 1.5 = 40 years 2 = 1...
November 2, 2014

Algebra
Wow, that is the second post in a row that your re-posted before checking if your first posting had been anwered. http://www.jiskha.com/display.cgi?id=1414981217
November 2, 2014

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