Tuesday
June 30, 2015

Posts by Reiny


Total # Posts: 30,304

math
Since volume of similar objects is proportional to the cube of their sides, your cubes will probably be too large e.g. suppose we have cubes of sides 1, 2, 3, 4, 5, .. their corresponding volumes are: 1, 8, 27, 64, 125, ...
April 11, 2015

algebra
the domain is the set of all first elements (the x's) and the range is the set of all the 2nd elements (the y's) I am sure you can plot those points
April 11, 2015

Math
if x = 5 or x = -3 then the equation could be (x-5)(a+3) = 0 or x^2 - 2x - 15 = 0
April 11, 2015

math
one angle ---- x other angle -- 4x+10 a) x + 4x+10 = 90 b) x + 4x+10 = 180 in each case , solve for x
April 11, 2015

MATHSS PLESE HELP
Vinny, I count 6 consecutive posts by you of rather diverse problems, some requiring knowledge of physics. I did the first one for you. You have shown no work or indication that you have tried these, and it looks like just a "homework dump". Where do your ...
April 11, 2015

MATHS
3x^2 - 8 = 3x - 2 3x^2 - 3x - 6 = 0 x^2 - x - 2 = 0 (x-2)(x+1) = 0 x = 2 or x = -1, but you can't make negative units, so x = 2
April 11, 2015

algebra
a/b = 2 then a = 2b we want (3a+6b)/(b-a) = (3(2b) + 6b)/( b - 2b) = 12b/-b = -12
April 11, 2015

math
75% amount --- x 30% amount --- 250-x .75x + .3(250-x) = .5(250) solve for x
April 11, 2015

maths
2x + 4/3 = 62/15 solve for x Just notice Damon did this 3 years ago http://www.jiskha.com/display.cgi?id=1324019336
April 11, 2015

Math
yes it is
April 10, 2015

Finance
The initial monthly payment is established on the assumption that everything stays the same. The major problem here is the fact that the interest period of compounding is different from the interest period of the payments. That is, the interest rate is compounded semi-annually...
April 10, 2015

Math
It would be a 7 by 2
April 9, 2015

Algebra: Quadratic Functions
change your equation to vertex form and all mysteries shall be revealed to you.
April 8, 2015

Algebra: Quadratic Functions
your equation is not correct, should be h = 112t - 16t^2 This is a parabola opening downwards You have to find the vertex, and A and B can be answered at that point hint: the t of the vertex is -b/(2a) plug that back into the equation to get h, the maximum let me know what you...
April 8, 2015

Math
Convince me that D is the correct answer
April 8, 2015

Math
Your result is already in the final stage before you can just start stating the answer. from the last line, z = 1 in the 2nd line 5y+3z = 13 plug in z = 1, then find y now you have y and z so plug those into the 1st line and you are done
April 8, 2015

Math
Precisely my point. Since you stated that the spinner was on green, it can't be on yellow, and prob(odd and yellow) = 0 So your question is bogus
April 8, 2015

Math
When you posted this earlier , to said it made no sense. I think you made some changes near the end and are now saying that the spinner is on green. But you want P(odd and yellow) so prob = 0 Always check your typing before submitting to make sure it makes sense and has no ...
April 8, 2015

algebra
width --- w length --- 2w - 5 Perimeter = 2 x width + 2 x length = ... area = (width)(length) = ... when w = 8 l = 16-5 = 11 take over
April 8, 2015

Geometry help
If by "regular triangle" you mean equilateral triangle, then each side is 30√3/3= 10√3 and sin60 = apothem/10√3 apothem = (√3/2)(10√3) = 15
April 8, 2015

geometry
Surely your text or your notes will tell you what these terms mean and how to change numbers from one form to another. What have you learned in class regarding these?
April 8, 2015

Calculus
Let t sec be the time since the balloon was directly above the bike, and let d ft be the distance between the balloon and the bike. According to my diagram, d^2 = (58t)^2 + (150 + 10t)^2 = 3364t^2 + 22500 + 3000t + 100t^2 = 3464t^2 + 3000t 2d dd/dt = 6928t + 3000 dd/dt = (...
April 8, 2015

calculus
I used to cut open a paper drinking cup in class when I was teaching this particular question. It was easy to see that the resulting arc was equal to the circular base of the cup and the "slant" height of the cup was the radius of the partial circle. Try this, and ...
April 8, 2015

Math
Would 4 x 1/7 equal 8/7 ?? Are you just guessing?
April 8, 2015

Math
The way your typed it, I do not understand the question.
April 8, 2015

Math
And what is the common factor of 3x and of 12 ??
April 8, 2015

Math didn't post problem right
I noticed you changed your divisor from 12 to 21 Don't you have a calculator ? Even an approximation of 1800/20 = 90 would have given you a clue about the right answer.
April 8, 2015

Math
Prob(5) = 1/6 prob(blue) = 1/4 what is (1/6)(1/4) ??
April 8, 2015

Math
Just checked by first calculation, should have been 72√3/2 or appr 62.4 My conclusion remains the same
April 8, 2015

Math
yes, they can case 1 : a triangular prism with an equilateral base of 12 cm per side, and a height of 10 cm volume = area of base x height = (1/2)(12)(12)sin60 = 72√3 or appr 124.7 cm^3 Notice the perimeter of the base is 36 and the height is 10 case 2: a rectangular ...
April 8, 2015

Math
You don't say if the sun is showing on its forward or its backwards leaning side. One triangle would have sides of 55.9m 90 m and an angle of 84.5° between simple application of the cosine law to find the distance between the end of the shadow and the top of the tower...
April 8, 2015

Math 141
two ways to get a sum of 3 either 12 or 21 our possible outcomes, sum ≤ 6 : 11, 12, 13, 14, 15 21, 22, 23, 24 31,32, 33, 41, 42 51 15 of them prob(your event) = 2/15
April 8, 2015

PRE - CALCULUS
type powers this way: (2x+5)^2 = 49 so 2x+5 = ±7 2x = 2 or 2x = -12 x = 1 or x = -6
April 8, 2015

PRE - CALCULUS
If you mean 3√((-4)^3) then = 2√-64 , which is not a real number
April 8, 2015

exponential equations
come on, this is the same as all the others of this type that you posted. What is your solution for this question?
April 8, 2015

exponential equations
400(2)^(72/d) = 6400 2^(72/d = 16 = 2^4 so 72/d = 4 4d = 72 d = 18
April 8, 2015

exponential equations
We did this for you this morning Why are you reposting it? http://www.jiskha.com/display.cgi?id=1428502111
April 8, 2015

Finite Math
let the rate be i 24000(1+i)^5 = 34616 (1+i)^5 = 1.44233.. take the 5th root of both sides to get 1+i = ..... isolate i and you are done
April 8, 2015

math
huh? isn't area = length x width ? so area = 8(6x+3) = 48x + 24 Trying to figure out how you could possibly come up with 9x+8
April 8, 2015

MATH
Find the perimeter in yards : use 2L + 2W change that to feet by multiplying by 3 Divide by 10 to get the number of gallons
April 8, 2015

Exponential Equations
You might want the equation: number = 1000 (2^(t/18) ) so when t = 180 number = 1000 (2^10) = 1000(2^10) , the same result that Damon got
April 8, 2015

algebra
You can generate a Pythagorean triple using the following "formula" take any values of m and n, where m > n then 2mn m^2 - n^2 m^2 + n^2 will form a Pythagorean triple e.g. m = 6 , n = 5 2mn = 60 m^2-n^2 = 11 m^2 + n^2 = 61 and 60^2 + 11^2 = 61^2 so 11, 60, 61 ...
April 8, 2015

math help
6^x 2-3^x.2^x 1/6^x-1 I will assume it is something like (6^x)^2 - (3^x)(2^x) ?? 1/( (6^x)^-1 = (6^x)^2 - 6^x ?? 6^x can't make out the last part (where I have ??), missing an operator like + or - or ..
April 7, 2015

Algebra
let y = 5^(3/4) then your expression becomes ( (5x)^(3/4) )^2 + 2(5^(3/4) + 1 = y^2 + 2y + 1 = (y + 1)^2 = ( 5x^(3/4) + 1)^2
April 7, 2015

math
i = .08/4 = .02 ----- because of "compounded quarterly" n = 5(4) = 20 ----- there are 20 quarters. plug into "amount of annuity" formula
April 7, 2015

Business math
careful, the payments are made at the beginning of each period, where the formulas we use assume that payments are made at the end of the period i = .12/2 = .06 n = 8(2) = 16 but we will use only 15 and I will assume that the first payment is $1200 is made NOW. PV = 1200 + ...
April 7, 2015

Algebra
This is just a "homework dump". Now, with which particular question did you run into difficulties? Show me the steps you took leading up to your difficulty. Btw, the cut-and-paste clearly did not work for the last two questions.
April 7, 2015

Math
distance now = 8.5 one week from now = 8.5(1.15) two weeks from now = 8.5(1.15)^2 = 11.24
April 7, 2015

Exponential Equations
1000(1+r)^2 = 1175 (1+r)^2 = 1.175 take √ of both sides 1+r = 1.08397.. r = appr .0840 or 8.40%
April 7, 2015

algebra
determinant of coefficient matrix 1 3 2 2 -1 -3 5 2 1 is -28 now replace the first column with the the constants coefficients 3 3 2 -8 -1 -3 9 2 1 and the determinant of that is -56 do a = -56/-28 = 2 now replace the 2nd column with the constants and find the determinant to ...
April 7, 2015

math
So the total score for all 100 students is 7710 Two more students added 125 for a new total of 7835 new average = 7835/102 = 76.8 2. total = 12 bb-players + 18 baseball players = 30 players but there were only 24 , so 6 must have been playing both sports. check: 12+18-6 = 24
April 7, 2015

Calculus
just notice I skipped the -2x term so our derivative should be . 2(2)dy/dt + 2(-1)(-4) - 2dx/dt + 6(-1)^2 dy/dt = 0 2(2)dy/dt + 2(-1)(-4) - 2(-4) + 6(-1)^2 dy/dt = 0 4dy/dt + 8 + 8 + 6dy/dt = 0 dy/dt = -16/10 = -1.6
April 6, 2015

Calculus
your 2(2)dy/dt+(2)(-1)(-4)+6(-1)^2=0 should have been 2(2)dy/dt + 2(-1)(-4) + 6(-1)^2 dy/dt = 0 4 dy/dt + 8 + 6dy/dt = 0 10dy/dt = -8 dy/dt = -4/5 I don't see any errors.
April 6, 2015

Calculus
use implicit derivatives .... 2x dy/dt + 2y dx/dt + 6y^2 dy/dt = 0 now just plug in the given stuff.
April 6, 2015

Calculus
Profit(x) = R(x) - C(x) = 60x - .5x^2 - 5x - 15 = -.5x^2 + 55x - 15 dPdt (x) = -x dx/dt+ 55 = -30(20) + 55 = .....
April 6, 2015

Calculus
same as your other question. check your work, that should have been √171 instead of √192 25 + y^2 = 14^2 y^2 = 196 - 25 etc
April 6, 2015

intermediate algebra
3/((x+3)(x-3))- x/(x-3)(x-3) + 1/(x+3) The LCD is (x-3)(x-3)(x+3) = (3(x-3) - x(x+3) + 1/((x-3)(x-3))/((x-3)(x-3)(x+3)) = .... take over
April 6, 2015

Calculus
you are right, I got my fraction upside down, sorry dy/dx = -2/√140 = appr -.169
April 6, 2015

Calculus
This is the classic example used by most textbooks in the introduction to Related Rates in Calculus. let the foot of the ladder be x ft from the wall, let the ladder reach y ft above the ground x^2 + y^2 = 12^2 2x dx/dt + 2y dy/dt = 0 or x dx/dt + y dy/dt = 0 given: dx/dt = 1 ...
April 6, 2015

math please help
done, check back to earlier post and correction
April 6, 2015

Math
I would make a sketch of each function on the same grid. Also they told you what to do in the hint, why not do that?
April 6, 2015

Math
Check for the solution and the correction I just made to your previous post
April 6, 2015

Pre-Calculus
I agree with you x^2+9x+20 = x^2 + 9x + 81/4 - 81/4 + 20 = (x+9/2) + 20 - 81/4 = (x+9/2)^ - 1/4
April 6, 2015

correction - math
I misread your c = 5.5 as c = 3.5 , sorry about that So AD should be 2.75 But AC is still greater than 2.75 so no real harm done, all you have to do is change the 3.5 to 5.5 and use the new values. The conclusion is still the same, but make sure you get the new angles.
April 6, 2015

math
First let's see if it is possible. Start with a base of BC, sketch an angle of 30° at B and draw a line BA = 3.5 sketch in an altitude from A to BC to meet BC at D sin30° = AD/3.5 AD = 3.5(1/2) = 1.75 Since AC > 1.75, it will be possible to draw the triangle. As...
April 6, 2015

AP CALC
then y = c e^(kt) when t = 4 4c = c e^(4k) 4 = e^ 4k 4k = ln4 k = ln4/4 y = 1500 e^((ln4/4)t) so when t = 3 y = 1500 (e^(3ln4/4) = appr 4243 check: at t=4 y = 1500 e^(4ln4/4) = 6000
April 6, 2015

geometry
let C be (a,b) by the midpoint theorem we know: (-3+a)/2 = 5 and (2 + b)/2 = -4 -3+a = 10 and 2+b = -8 a = 13 and b = -10 so A is (-3,2) , C is (13,-10), and the midpoint between them is B(5,-4) You should have seen that your answer is incorrect as soon as you graphed it. (I ...
April 6, 2015

Algebra
You probably do not recognize that as a "sum of cubles" facoring result, if you do, you can jump directly to the final line, otherwise .... So let y = 5x^(1/3) , then 25x^(2/3) can be written as (5x^(1/3))^2 = y^2 so we have (y + 1)(y^2 - y + 1) = y^3 + 1 = (5x^(1/3...
April 6, 2015

Math
the official radius of a ping pong ball is 20 mm or 2 cm so the volume of a ball is (4/3)π(2^3) = appr 33.5 cm^3. which Ms Sue has correctly as 2.045 inches^3 but the balls will not "stack" nicely. Did you ever look at a stack of cannonballs at some fort? If we ...
April 6, 2015

Math
volumes of similar solids are proportional to the cube of their sides so volume of original = 8m^3 volume of new is 72 m^3 so let's take the smallest dimension of 1 m , since it is a unit dimension. 8/72 = 1^3/x^3 8x^3 = 72 x^3 = 9^(1/3) x = 9^(1/3) = appr 2.08 So, he ...
April 6, 2015

Algebra
= t + 4t^(1/2) + 4 or = t + 4√t + 4
April 6, 2015

math
You haven't even defined any variables, so what equations did you get?
April 6, 2015

Finite Math
treat P(R and S) as a variable, suppose it is x, then your first equation becomes P(R or S) = P(R) + P(S) - x , .... you have a typo here .64 = .38 + .52 - x x = .9 - .64 x = .26 P(R and S) = .26
April 6, 2015

Math Check
Did you even look at my reply to your same question which you posted less than 1 hour ago ? http://www.jiskha.com/display.cgi?id=1428346534
April 6, 2015

Math Help Please!
Without even doing any calculation, since there is such a large difference in the interest rates, it should be obvious that the simple interest plan should be the better of the two. check: at simple interest I = 2000(.13)(4) = 1040 so amount in your account = 3040 at compound ...
April 6, 2015

math
look at my concern about this problem in your earlier post
April 6, 2015

Math: Geometry
a) the block was (15)(8)(5) cm^3 = ..... you have to know the volume of a cylinder , which is v = π r^2 h You don't say in which direction the holes are drilled, so I can't continue
April 6, 2015

Math
If this relation were to be even remotely true, we could form a ratio .... 18 months/36 inches = 60 months/x inches 18x = 2160 x = 120 inches or 10 ft tall (can you see how absurd your question is ???? ) Also in h = 2c , you don't define what h and c stand for.
April 6, 2015

algebra
first step: (a^3 - b^3)(a^3 + b^3) second step: we can factor the sum and difference of cubes, should be in your notes or text = (a-b)(a^2 + ab + b^2)(a+b)(a^2 - ab + b^2)
April 6, 2015

maths
That is, 8x - 163 = 3x -13
April 6, 2015

math
mmmmhhh , been on this earth over 75 years, and guess what, each of those years had 4 seasons (4 quarters) , so 4 years will have 16 quarters. notice that the interest rate is compounded quarterly, so we need the rate per quarter. That is i = .06/4 = .015 n = 16 I have no clue...
April 6, 2015

math
i = .06/4 = .015 n= 4(4) = 16 Present value of payment option = 2400(1 - 1.015)^-16)/.015 = 33915.03 Well, what do you think ?
April 6, 2015

math
Prob(green, then yellow) = (5/30)(8/29) = 4/87
April 6, 2015

Math
-8x^2-8x-2=0 or 4x^2 + 4x + 1 = 0 discrm = 16 - 4(4)(1) = 0 thus there is one solution. check: 4x^2 + 4x + 1 = 0 (2x + 1)^2 = 0 2x+1 = 0 x = -1/2
April 6, 2015

Precal
change 9 to base 3 as 9 = 3^2 (3^2)^x^2 = 3^(-5x - 2) so : 2x^2 = -5x-2 2x^2 + 5x + 2= 0 (2x + 1)(x + 2) = 0 x = -1/2 or x = -2
April 5, 2015

calc 1
Look at the solution I gave Ryan for an almost identical problem as yours http://www.jiskha.com/display.cgi?id=1427010949
April 5, 2015

Math
I think Steve is missing part of the formula and/or using the wrong formula. PV = paym(1 - (1+i)^-n)/i so here PV = 900(1 - 1.02^-16)/.02 = $12,219.94 So he should take the payment option.
April 5, 2015

algebra
I will read that as: (x+3)/x^3 ÷ 6/(x-3) then ... = (x+3)/x^3 * (x-3)/6 = (x^2 - 9)/(6x^3)
April 5, 2015

math
You don't tell me what your x represents, but from your equation I conclude that you defined x to be each of the 3 parallel sides and y as the length of the whole field then area = xy = x(2250 - 1.5x) = -1.5x^2 + 2250x your A(x) = 2250 - 1.5x^2 is almost correct, but it is...
April 4, 2015

math
divide your equation by 50 20x + 10y + z = 200 remember that x, y, and z must be positive whole numbers. Are we allowed to have zero of any of them ???? I will let you decide that z = 200 - 20x - 10y maximum value of x has to be 9, (if x=10, z = 0) maximum value of y has to be...
April 4, 2015

algebra
One small change from your previous problem. Instead of 46 minutes you now have 54 minutes.
April 4, 2015

algebra
distance outside city --- x distance inside city ---- 33-x time = distance/rate x/50 + (33-x)/30 = 46/60 solve for x (I suggest multiplying each of the 3 terms by 300)
April 4, 2015

math
points depend on the number of prizes
April 4, 2015

Trigonometry
first answer line should be 1. y = 2 sin 4(x - π/8) + 1 or y = 2 sin (4x - π/2) + 1
April 4, 2015

disagree - rigonometry
I disagree with your phase shift in general: y = a sin k(x - d) + c the phase shift is d. Notice that the period indicator k is factored out In your answer we have ... sin(4x - π/8) ... or ... sin 4(x - π/32)... So the phase shift of your equation would be π/32 ...
April 4, 2015

maths
circumference = 40π cm so in one minute would cover 50(40π) or 2000π cm to cover 6.28 km or 628000 cm would take 628000/(2000π) minutes , or 99.949.... minutes, which is appr 1hr and 40 minutes
April 4, 2015

geometry
let the third side be x , where x is a positive number FACT: the sum of any two sides of a triangle must be greater than the third side, so 22+34 > x AND 22+x > 34 AND 34+x > 22 clearly 34+x is always > 22, so for the other two ... 56 > x AND x > 12 or 12 <...
April 3, 2015

geometry
Don't all three angles add up to 180° ? Use this fact to form your equation, then solve it
April 3, 2015

math discrete 2
Since it is linear, we can just "reverse" our steps. e.g. for g(x) , for any x, the first thing we do is multiply it by 4 and then subtract 5 now doing this backwards, start with an x, add 5, then divide that be 4 so g^-1 (x) = (x+5)/4 standard method: step1 : ...
April 3, 2015

math discrete
h◦(g◦f) = h(g(f(x) ) ) = h(g(4x^3 - 5) ) ) = h(2(4x^3 - 5)) = ( 2(4x^3 - 5) )^2 manipulate this if needed. testing with some value, say x = 2 according to my result: (2(32-5))^2 = 2916 long way: f(2) = 27 g(27) = 54 h(54) = 2916
April 3, 2015

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