Sunday
April 20, 2014

Posts by Reiny


Total # Posts: 26,034

algebra 1
Here is a graph of the situation. http://www.wolframalpha.com/input/?i=plot+y%3D-0.05x+%2B+12+%2C+-40%3Cx%3C40 The way it is stated the equation makes little sense to me. Is x the time relative to Sept 21 ? Is -40<*<40 supposed to mean -40 < x <40 ? that is, are yo...

algebra 1
Last night , I had given you a full explanation, set-up and even the solution for this problem, even though it only asked for the two inequations at the beginning of my solution. http://www.jiskha.com/display.cgi?id=1385177236 and you responded with, I am confused. What part d...

cal
I think you meant: f(x) = x/(x^2 + 1) (or else why not just reduce it to f(x) = 1/x + 1 ? ) for concave upwards, f ''(x) > 0 f'(x) = (1 - x^2)/(x^2 + 1)^2 using the quotient rule and again f''(x) = 2x(x^2-3)/(x^2+1)^3 so when is f''(x) positive ?...

math
Huh ? What question above ?

Math
use my favourite stats webpage http://davidmlane.com/hyperstat/z_table.html make sure you click "area from a value" enter 20 as the mean 4 as the sd click on "between" and enter 9.5 and 23 calculate to get 0.769

algebra 1
Aren't they supposed to be in-equalities? profit = revenue - expenses = 100x + 5y - 30x - 2y = 70x + 3y but 100x + 5y - 30x - 2y ≥ 400 70x + 3y ≥ 400 also 30x + 2y ≤ 200 15x + y ≤ 100 " Marissa can sell up to 8 framed photographs" --- >...

math
jhon: i want to add 34+85% i tryed it and i got 62.9 Reminds me of one of my favourite Bert & Ernie cartoons of years ago: temperature: 29° time : 6:15 ---------------- total: 6 : 44

cal
even though both Jai and I had the same answer, which is different from the one you picked ? Where would the 8 even come from ????

cal
f(x) = x^2 + x^(1/2) f ' (x) = 2x + (1/2)x^(-1/2) f '' (x) = 2 - (1/4)x^(-3/2) or 2 - 1/(4x√x) explanation: (x^(-3/2) = 1/x^(3/2) = 1/(x^(1/2)^3 = 1/(√x√x√x) = 1/(x√x)

Math help please
well, zero out of three is not that great. 1. did you notice 4^0 = 1 4^1 = 4 4^2 = 16 4^3 = 64 and 4^4 = 256 ?? 2. The height of the tree in my backyard "depends" on how long it has been there, so .... 3. suppose we have an area of 20 cm^2 and it stays at 20 if the w...

math(help)
1. what is 1/6 + 2/6 2. what is 8/8 - (4/8 + 1/8) 3. what is 7/8 - 5/8 4. what is 11/20 - 9/20

Math
Some rational numbers are integers. (all I need is one example) fraction--- 6/2 ineger ---- 2 is 6/2 = 2 ? The circumference of a circle varies directly with its radius f(x) = .08x^3 + .6x + 2.8 - certainly not a quadratic , (I see a cub) - I certainly don't see any variab...

math
You posted this before, it made no sense then, and it makes no sense to me now. what does x ≥ -13 , -13 mean ?

math
What a lot of extra verbiage to state the simple question: How many place settings can I make from 3 kinds of place mats, and 3 kinds of napkins (she can't use the orange ones, since she has only 3) Since all the setting have to be the same, we just have to find one number...

Pre-Calc Help!!!
LS = (tanx - tan(π/4)/(1 + tanx(tan(π/4)) ) = (tanx - 1)/(1 + tanx) = RS I used the identity tan(A-B)= (tanA - tanB)/(1 + tanAtanB) and the fact that tan π/4 = tan 45°= 1

Math
your equation says: y = -5 now in the given point (-3,1) is the y value equal to -5 ?

Geometry
actually, there is an infinite number of solutions one of the properties of a circle is that a triangle is formed with the diameter as a base and the other point on the circle, you will always have a right angle. so the centre would be (5,3) and the radius would be 2√2 e...

cal
some patterns you should just recognize. I know how to differentiate and integrate sin (?), but in both cases the derivative of the "angle" which would be the x from the x^2 has to be considered. Sure enough, the derivative of x^2, which would be 2x , is hanging arou...

cal
wouldn't that just be 5 cos(x^2) + c ?

Geometry
notice the points given form a horizontal line, so the length of the side must be 7 the x coordinate of the third point must be midway between the two points (simple geometry, look at your sketch) let the third point be P P is (-3/2, y) so the distance from P to (2,3) must be ...

math(help)
29/59 = appr .4915.. or about 1/2

math in focus
number of girls --- x number of boys --- x+121 number of females -- y number of males ---- 3y number of women = y - x number of men = 3y - x - 121 "5/6 of the males were boys " ---> (5/6)(3y) = x + 121 15y = 6x + 726 6x - 15y = -726 2x - 5y = -242 ---- A "2/3...

Calculus Help!!!
notice that one parabola opens up, the other down. their intersection ..... x^2 - c^2 = c^2 - x^2 2x^2 = 2c^2 x^2 = c^2 x = ± c ---- y = 0 in both they intersect at (-c,0) and (c,0) using symmetry area = 2∫(2c^2 - 2x^2) dx from 0 to c = 2(2c^2 x - (2/3)x^3) | from...

Kelly - Amy - Chrissy Calculus
Why are you switching names ???? Follow the method I showed you in the other two questions of this type. Did you look at the solutions? Let me know how far you get.

Algebra 1
better form .... -2x + y = 2 ---> 2x - y = -2 4/3x+y=19/3 ----> 4x + 3y = 19 1/2x+y=-13/2 ----> x + 2y = -13 9/7x+y=-3/7 ---->9x + 7y = -3 7/9x+y=-10/3 ----> 7x + 9y =-30 can you see what I did? A proper way to write equation in standard form: - no fractions sho...

Chris - Amy -Calculus Area between curves
Why are you switching names ?? find the intersection; from the first: x = 3 - 3y into the 2nd: y^2 - (3-3y) = 1 y^2 + 3y - 4 = 0 (y+4)(y-1) = 0 y = -4 or y = 1 in x = 3-3y .... if y = 1, x = 0 ---->(0,1) if y = -4 , x = 15 , ---> (15, -4) Your sketch should look like thi...

Calculus-Area between curves
first of all reduce the equation to simplest form: y = 2√x y = 5 y + 2x = 4 Your sketch should look like a "triangle" with one side slightly curved see: http://www.wolframalpha.com/input/?i=plot+y%3D2*sqrt%28x%29+%2C+y%3D5+%2C+y%2B2x%3D4 we need all the interse...

Algebra 1
slope = (4-2)/(5-(-1)) = 1/3 pick (5,4) y-4 = (1/3)(x-5) times 3 3y - 12 = x - 5 x - 3y = -7 check: does the point I didn't use satisfy the equation? for (-1,2) LS = -1 - 3(2) = -7 = RS ......... all is good!

Finance
amount in 2000 = 2000(1.015)^20 = 2693.71 plus the extra 500 in year 2000 =3193.71 This will earn for 4 years final amount = 3193.71(1.0175)^16 = 4215.47

algebra
Trying x = ± 1, ± 5 I get a zero when x = -1 by synthetic division: (x+1)(x^4 + 2x^3 - 4x^2 - 10x - 5) = 0 well, what do you know, x = -1 works again, so (x+1)(x+1)(x^3 + x^2 - 5x - 5) = 0 grouping the last part (x+1)(x+1)( x^2(x+1) - 5(x+1) ) = 0 (x+1)(x+1)(x+1)...

algebra
so 50 = -t^3 + 34t^2 - 284t + 490 t^3 - 34t^2 + 284t - 440 = 0 I tried t = ± 1, ± 2 and sure enough when t = 2, I had a solution using synthetic division, (t-2)(t^2 - 32t+ 220) = 0 (t-2)(t-10)(t-22) = 0 t = 2 or t = 10 or t = 22 Since the ride lasted 25 minutes, ...

cal
f(x) = x^-2 - 2x - 8 f ' (x) = -2x^-3 - 2 f '' (x) = 6x^-4 extrema: -2/x^3 = 2 x^3 = -1 x = -1, f(-1) = 1 - 2(-1) - 8 = -5 at x = -1, f ''(-1) is > 0, so (-1,-5) is a minimum my answer confirmed by http://www.wolframalpha.com/input/?i=plot++y+%3D+1%2Fx%5...

check: Algebra 1
I assumed your constant would have been correct, wrong assumption. go with kuai's solution, but write it as x- 2y = -7

Algebra 1
It is considered "poor form" to have the equation in standard form start with a negative x or containing fractions. so the 1st one I would write as x - y = -8 the last one: firs of all it should have been (-1/2)x + y = 23/2 multiply each term by -2 x - 2y = -23

geometry
correct

geometry
dodecagon --- 12 sides It must be regualar, that is, all sides must be equal and all 12 interior angles are equal. sum = 180(n-2) so each angle = 180(n-2)/n for 12 sides: each angle = 180(12-2)/12 = 150° you do the one with 20sides

6th grade math
nope http://www.wolframalpha.com/input/?i=plot+%281%2C5%29%2C+%282%2C5%29%2C+%283%2C5%29%2C+%284%2C5%29 notice all their y values are the same, y = 5 so it is a horizontal line

math
Your question makes no sense to me What is $150 ? Is the 8% rate compounded monthly? What is the $12.87 supposed to represent? You did not define m, r and t

algebra
Is what answer true or false ?? 8x-2 = -9+7x x = -7

LOL @ Steve --
Hilarious Captain: What happen ? Mechanic: Somebody set up us the bomb. Operator: We get signal. Captain: What ! Operator: Main screen turn on. Captain: It’s you !! CATS: How are you gentlemen !! CATS: All your base are belong to us.

MATH
Great read: Outliers by Malcolm Gladwell

College Algebra
your equation only has one variable. 5x + 3y = 60 3y = -5x + 60 y = (-5/3)x + 20 the y intercept of 20 ( or y = 20) gives you the number of gumballs (y) you can buy for 60 cents if you buy zero mints.

cal
f'(x) = 6x^2 - 6x - 12 = 0 for a max/min (critical value) divide by 6 x^2 - x - 2 = 0 (x-2)(x+1) = 0 x = 2 or x = -1 so, yes, x=2 is a critical number, (the other is x = -1) f '' (x) = 12x-6 f(2) = 2(2^3) - 3(2^2) - 12(2) + 18 = -2 f '' (2) = 24-6 > 0 si...

clarification - math(help)
Just because one of the numbers is a prime, does not mean the fraction is in lowest terms. e.g. 13/26 = 1/2 21/7 = 3 the numerator and denominator have to be "relatively prime", that is, no whole number exists that divides into both of them

math(help)
Why didn't they just ask, " Is 138435 evenly divisible by 3 ? " yes it is. is 38/53 in lowest terms? yes it is, since no whole number divides into both 38 and 53 here is a little-known trick: find a key a b/c on your calculator enter: 38 a b/c 53 = you will g...

Maths
I will assume that the building with side BC is on top of the cliff and A is at the bottom of the cliff. step1: tan44= AB/200 AB = 200tan44 so AC = 80 + 200tan44 let angle CPA = Ø tanØ = AC/200 = (80 + 200tan44)/200 tanØ = 1.365 Ø = 53.79°

cal
I will assume that you meant f(x) = 2x^(3/2) - 6x^(1/2) (or else we could just divide out the 2's in the first term) f ' (x) = 3x^(1/2) - 3x^(-1/2) f '' (x) = (3/2)x^(-1/2) + (3/2)x^(-3/2) or (3/2)( 1/√x + 1/(x√x) )

6th grade math
1. all three are correct 2. "they ate 1/5 of the bag" is not clear Did they eat 1/5 of a full bag, or Did they eat 1/5 of what was in the bag when she arrived?

Algebra 1
y+4 = x-2 y = x - 6 ---> usually called the y intercept - slope form or x - y = 6 ---> some texts call this standard form and this x-y - 6 = 0 ---> general form

Algebra, URGENT!!!
1. x^2 + (x+6)^2 = 8^2 x^2 + x^2 + 12x + 36 - 64 = 0 2x^2 + 12x - 28=0 x^2 + 6x - 14 = 0 x^2 + 6x = 14 , completing the square .... x^2 + 6x + 9 = 14+9 (x+3)^2 = 23 x+3 = ± √23 x = -3 ± √23 but x has to be positive so x = √23 - 3 so one leg is &...

College Algebra
A = 25000 e^(.06(5)) A = 25000 e^.3

home school
let the numbers be x and y x+y = 42 ---> y = 42-x xy = 185 --->x(42-x) = 185 42x - x^2 - 185 = 0 x^2 - 42x + 185 = 0 (x-37)(x - 5) 0 x = 37 or x = 5 then y = 42-37 or y = 42-5 y = 5 or y = 37 (symmetric solution) the two numbers are 5 and 37

Algebra NEED HELP ASAP!!!!!!
T = 4h + 72 , 0 < h < 12, where h is the number of hours at noon , h = 6 T = 72 + 4(6) = 96

cal
did you mean it the way you typed it, or did you mean f(x) = √(x+2) ? I will assume f(x) = √(x + 2) judging by the values of the interval first take the definite integral of the function = ∫(x+2)^(1/2) dx from 1 to 7 = (2/3)(x+2)^(3/2) | from 1 to 7 = (2/3)9^...

Math Properites
= (3.4)(3.8)(10^5)(10^-9) = 12.92(10^-4) = 12.92/10000 = .001292

TRIANGLE SIMILARITIES RATIOS AND PROPORTIONS
The key to this question is to realize that all the right -angled triangles are similar, and have the ratio of 3:4:5 in the length of their sides. Mark the two angles in triangle BCD with o and x ( you should be able to see that since XD | BC , so you can mark XDC as o and DCX...

Pre-Calculus
did you notice that f(x) = (x-9)(x-2)/(x-9) ?? = x-2, x ≠ 9 So for all values of x except x=9 the given function reduces to f(x) = x-2 which is a straight line. when x = 9, the original gives you 0/0 which is indeterminate, while the reduced function gives you (9,7) So t...

algebra 2
Prob(cheese, then turkey) = (6/15)(5/14)= = 30/210 = 1/7

MATHS
all multiples of 7 are $1 7, 14, 21 ------- $3.00 all multiples of 6 are .50 6,12,18,24,------- 4(.50) = $2.00 all multiples of 5 are .20 5,10,15,20 ---- 4(.20) = $.80 all multiples of 4 are .10 4,8,12,16,20,24 but the 12, 20 and 24 have been changed, so only the 4,8, and 16 c...

Advanced Funtions
if either x or y , or both = 0

Advanced Functions
They were the most obvious ones.

Advanced Functions
sin 60° = √3/2 cos 30° = √3/2 sin 120° = √3/2

PRECALCULUS
solve both as quadratics that factor 1. 2cos^2 x - 5cosx + 2 = 0 (2cosx - 1)(cosx - 2) = 0 cosx = 1/2 or cosx = 2 but cosx = 2 is not possible, since -1 ≤ cosx ≤ +1 for cosx = 1/2, since it is positive, x could be in I or IV x = 60° or x = 360-60 = 300° 2. ...

Advanced Functions
if cosx = 5/13, (recognize the 5,12,13 triangle ?) sinx = 12/13 tanx = 12/5 if cosy = -5/13 and y is in III siny = -12/13 tany = 12/5 2sinx+2siny+2cosx-2tanx+tany+2cosy = 2(12/13) + 2(-12/13) + 2(5/13) -2(12/5) + (12/5) + 2(-5/13) = - 12/5 or -2.4

Trig - Law of sines and cosines
I started with AB, the vertical diagonal of the square. I then drew square ALMN At M, I drew the base BC of the equilateral triangle perpendicular to AM, letting BM = MC = 2 Joi AB and AC for the triangle. Let the intersection of ML and AB be P, and the intersection of MN and ...

algebra 2
What is your question? What does "3/4 Six lots" mean?

algebra
BTW, Steve answered you yesterday when you posted it then. Did you not look at his answer?

algebra
prob(rain on Sat and Sun) = (10/100(30/100) = (1/10)(3/10) = 3/100 or 3%

Algebra
multiply each term by ab, the LCD bx - ab = ay y = (bx - ab)/a or just multiply both sides by b bx/a - b = y , which is the same as my first result

algebra
let the amount invested at 11% be x so .11x + .12(x+4000) = 940 .11x + .12x + 480 = 940 .23x = 460 x = 2000 So originally you had $2000 in the 11% account and $6000 in the 12% account at the end you had 2220 and 6720 respectively check: 2220+6720-8000 = 940

Geometry (math)
True No need to draw a figure, just look at the screen on your computer. let s be the top of the screen let q be perpendicular of your screen, how about the left side? let p be the bottom of your screen Is the top of your computer screen not parallel to its bottom?

Math
geesh, forgot to put D) in front D) which means that for every increase of 1800 feet, the temperature would decrease by 1° or for every decrease of 1800 ft , the temperature would rise by 1° F B) so how did Tessa get +.9/-.5 ? look at the bottom number of -.5. where di...

Math
clearly Gemma used the first two pairs, just check the calculations. B) which difference in the first elements would give you -.5 ?? c) no matter which pair you take you get a slope of -1.8 or -1.8 : 1 or -1800 ft : 1° F which means that for every increase of 1800 feet, th...

math
prob(yellow) = x/(20+x) but we know this is 1/6 x/(20+x) = 1/6 6x = 20+x x = 4 so there are 24 balls, of which 9 are blue so Prob(blue) = 9/24 = 3/8

Math questions
think of 8 as the slope and (12,240) as an ordered pair for this relation y = -8x + c at (12,240) 240 = -8(12) + c c = 336 y = -8x + 336 so when x = 0, y = 336 Where was he when x = 0 ???? at ground, y = 0 solve 0 = -8x+240 8x = 240 etc ....

algebra
What do you think? I don't see your choice of answer for any of them.

Pre-Calculus
since the line is perpendicular, their slopes are negative reciprocals of each other, that means, they must be OPPOSITE in sign so first slope = -3/2 2nd slope = +2/3 y-2 = (2/3)(x-4) 3y-6 = 2x-8 3y = 2x - 2 y = (2/3)x - 2/3

Math Help
#2 is correct #3 solving your 2 equations: 1st times 2: 8b+6n=47 2nd times 3: 15b+6n=64.5 subtract them: 7b = 17.5 b = 2.5 sub back in ----> n = 4.5 necklace costs $4.50 and bracelet costs $2.50 so buying just one each = $7.00

Math Help
first one: your equation: B = 22 +11.5w , where B is the balance, and w is the number of weeks or y = 22+11.5x to make it fit your x = 8 your friend: y = 218-13x if x = 8, you will have 22+11.5(8) = 114 your friend has 218-13(8) = 114 What do you think? Give the other two a sh...

Math
number of small posters x number of large posters y cost of small posters 240/48 = 5 cost of larger posters 240/30 = 8 5x+8y=240 to graph it, I would use intercepts let x = 0, y = 30 --->(0,30) let y = 0 , x = 48 ---> (48,0) slope = (0-30)/(48-0) = -5/8 For each reductio...

Geometry
Use the results of the ratio properties I gave you in your previous post

geometry
For the question to be "workable", AF is probably the median, with F on BC remember the centroid cuts the median in the ratio of 2:1, or AG:GF = 2:1 then FG:AF = 1:3 (x+8)/(9x-6) = 1/3 9x - 6 = 3x + 24 6x = 30 x = 5

My fuzzy thinking - math
Forget my previous post, r could be 1.5 my program line 60 should say: 60 if (b*c*d)^2 = (a*b*c^2*d*e) then print a;b;c;d;e and I got 64 96 144 216 324 80 120 180 270 405 96 144 216 324 486

math
I think I missed the obvious Since a,b,c,d,e are integers in GS, the smallest value of r is 2 a - b - c - d - e 51 102 204 408 816 52 104 ... 53 .... infinite number of choices for a so... still a silly question

For Steve - math
Crazy question. Agree with you, there has to be more As it stands: b/a = c/b and c/b = d/c and d/c = e/d b^2 = ac , c^2 = bd , d^2 = ed then b^2 c^2 d^2 = abcde I then ran this "primitive" BASIC program 10 for a = 50 to 100 20 for b = 51 to 100 30 for c = 52 to 100 4...

Calculus
Write it as f(x) = 7x^-2 - 6x^-6 F(x)= -7x^-1 + (6/5)x^-5 + c F(2) = -7/2 + (6/5)/2^5 + c = ......

Calculus
let the side of the square be x let the side of the triangle be y 4x + 3y = 40 x = (40-3y)/4 height of triangle from the 30-60-90 triangle ratio = √3/2 y area of triangle = (1/2)(y)(√3/2 y) = (√3/4)y^2 area of square = [(40-3y)/4]^2 = (1600 - 240y + 9y^2)/16 ...

TO ANY MATH HELPERS
1. from the 1st equation: x = 3y+1 into the 2nd: 3(3y+1) - y +1 = 0 9y + 3 - y +1 = 0 8y = -4 y = -1/2 sub into 2nd: 3x - (-1/2) + 1 = 0 3x = -3/2 x = -1/2 Do #2 the same way from the 2nd: y = 2x+4 etc (Just stating the answers is not acceptable and serves no purpose)

math and physics
asks for login and password

math
just did it http://www.jiskha.com/display.cgi?id=1384818273

math
36 = 1x36 = 2x18 = 3x12 = 4x9 = 6x6 = 9x4 = ....

Math
1 more than half of x should be x/2 + 1

math
To add/subtract something, they must be in the same units e.g 5 apples + 8 oranges = 13 appleoranges? so 2 hrs, 45 minutes = 2 + 45/60 = 2.75 hrs 3hrs, 57 minutes = 3 + 57/60 = 3.95 hrs now you can add them: 2.75+3.95 = 6.7 hrs = 6 hrs + (7/10)(60) minutes = 6 hrs, 42 minutes ...

math
As an after-thought ..... Tn = T(n-1) + 4 , T1 = -40 , n > 1 In the recursive notation, the initial value has to be included or else you can't begin your sequence.

Precalculus
tanØ secØ = tanØ tanØ secØ - tanØ = 0 tanØ(secØ - 1) = 0 tanØ = 0 or secØ = 1 if tanØ = 0 Ø = 0, 180°, 360° ... , 180k° , where k is an integer if secØ - 1 then cosØ =...

Precalculus
sec(Ø + 81) = 2 cos(Ø + 81) = 1/2 I know cos 60° = 1/2 so Ø+81 = 60 or Ø+81 = 300° Ø = 60-81 = -21° or Ø = 219° now the period of cos(Ø+81) = 360° so adding 360 will give me another answer so Ø = -21 +...

math
lots of missing information What was the rate of interest? Did he make any monthly payments? Did he make not payments except the one at the end of 31 months?

Math-Algebra
A direct square variation is a quadratic Given any 3 points , I can find that quadratic, but we can't "force" a fourth point on it. e.g A = 20.115r^2 - 101.835r + 135.78 produces the first 3 points , but not the last one

Math-Algebra
What is the topic for this question? Are you learning about "curve fitting" ?

Math-Algebra
Not enough data to see a pattern http://www.wolframalpha.com/input/?i=plot+%282%2C12.57%29%2C+%283%2C11.31%29+%2C+%284%2C50.28%29%2C+%285%2C78.56%29

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