Tuesday
April 21, 2015

Posts by Reiny


Total # Posts: 29,638

math
All three are correct.
April 14, 2015

Math
area = 2(12.7 x 7.5) = ... ft^2 divide that by 33 to get the number of shingles. Remember to round up , since you can't buy a partial bundle then multiply be 29.95 to get the cost
April 14, 2015

Maths!!
I would sub in the first values for F and L to get an equation with a and b then sub in the second set to get another eqution in a and b Now that you have two equations in a and b, solve for a and b. Now you have the actual equation, sub in L = 6.5
April 14, 2015

Maths
If you stick to the same name, it is easy to find your previous posts. Just click on your name in the list.
April 14, 2015

Maths
http://www.jiskha.com/display.cgi?id=1428740268
April 14, 2015

Maths
Is that you Vinny ? http://www.jiskha.com/display.cgi?id=1428740896 i) for time taken, you said it was 12 seconds ii) the hint was to se h1 = h2 , well ??? t^2 + 1 = 4 - t t^2 + t - 3 = 0 solve as a quadratic, reject the negative value of t
April 14, 2015

math
That is one of the longest run-on sentences I have ever seen. Is the . key stuck on your keyboard? "A5-digit number has 7 in its place" ????? looks like a typo, ..... let the number be abcde "The hundreds place digit is 4 times the digit at once place" , ...
April 14, 2015

dai so
I assume you want to prove that it is an identity. LS = (sin^2 x + cos^2 x + 2sinxcosx)/(cos^2 x - sin^2 x) = (sinx + cosx)^2 / )(cosx+sinx)(cosx-sinx)) = (sinx + cosx)/(cosx - sinx) RS = (tan π/4 + tanx)/( 1 - (tan π/4)(tanx) ) = (1 + tanx)/(1 - tanx) = (1 + sinx/...
April 14, 2015

maths
the 7 on the left represents 70,000 The 7 on the right stands for 7
April 14, 2015

Calculus
a) did you differentiate with respect of t, and then sub in t = 5 ? b) P(x) = R(x) - C(x) = 32 ln(5x+3) - x/4 P ' (x) = 32(5/(5x+3)) - 1/4 = 0 for max/min situation 160/(5x+3) = 1/4 5x+3 = 640 etc
April 13, 2015

calculus
A = π r^2 dA/dr = 2πr so when r = 4 dA/dr = 8π
April 13, 2015

Pre-Calculus
correct
April 13, 2015

calculus
At a time of t minutes, let the height be h cm V = π r^2 h = 16π h dV/dt = 16π dh/dt but dh/dt = 2 cm/min , and the height is not an issue, since the variable h does not appear in dV/dt dV/dt = 16π(2) = 32π cm^3/min
April 13, 2015

Calculus
y=(cos(x)(x^2+9)^(2/3)/(sqr(x^3+2)) take ln of both sides ln y=ln ( (cos(x)(x^2+9)^(2/3)/(sqr(x^3+2)) ) by the rules of logs ln y = ln cosx + ln (x^2 + 9)^(2/3) - ln (x^3+2)^(1/2) = ln cosx + (2/3)ln (x^2 + 9) - (1/2)ln (x^3 + 2) now differentiate ... y' /y = sinx/cosx + (...
April 13, 2015

Math
1 km = .621371 miles 90 km = 55.923.. miles so 90 km/h = 55.923 mph (had that exact problem a few weeks back when I drove about 4000 km through the US with my km/h speedometer car)
April 13, 2015

geometry
Looks like 3 strikes, none are correct slope AB = (3-0)/(2-(-2)) = 3/4 slope AC = (-1-0)/(5-(-2)) = -1/7 slope BC = (-1-3)/(5-2) = -4/3
April 13, 2015

Pre-Calc
You must make an effort to memorize the formulas. (I suggest you memorize the pattern) cos(A+B) = cosAcosB - sinAsinB Notice you have that pattern in cos 12° cos 18° − sin 12° sin 18° = co(12+18) = cos 30 which you should have memorized as √3/2 from...
April 13, 2015

Math
Does that sentence make sense to you?
April 13, 2015

Pre - CALCULUS
I will assume your ellipse is x^2/36 + y^2/11 = 1 so a = 6 and b = √11 with the foci along the x-axis for that kind of ellipse, c^2 = a^2 - b^2 = 36 - 11 = 25 c = ± 5 thus the foci are (5,0) and (-5,0)
April 13, 2015

math
This is a GS where a = 36 , r = 1/2 term(n) = a r^(n-1) term(12) = 36(1/2)^11 = 36(1/2048) = 9/512
April 13, 2015

Pre Algebra Probability
no, the events are independent, so you multiply the probabities of each event urn1, prob(red) = 14/24 urn2, prob(red) = 11/15 prob(red and red) = (14/25)(11/15) = 77/180 btw, an urn is an ancient clay pot or jug. e.g. read: Ode on a Grecian Urn by John Keats
April 13, 2015

repeating decimals
I answered this for you, you even thanked me for it. Why are you reposting the same question?
April 12, 2015

math
isn't area = length x width ? so ... area = (x^2 - 2x + 8)(2x^2 + 5x - 7)
April 12, 2015

Math plz help
let x = 3.909090... multiply by 100 , (because I have 2 digits repeating, thus 2 zeros in 100, had there been 3 digits repeating, I would have mulitplied by 1000) 100x = 390.909090... subtract the original: 99x = 390.9090... - 3.909090.. 99x = 387 x = 387/99 = 43/11
April 12, 2015

Algebra
√(15/x^3) , (your question ) is not equal to √15/x e.g. let x = 2 √(15/x^3) = √(15/8) = 1.3693.. √15/x = √15/2 = 1.93649... test x = 2 in both of my answers, it works
April 12, 2015

Algebra
Really nothing to "solve" here, since there is no equation. You can rewrite it in several ways, here is one way: √(15/x^3) = √15/(x√x) or you could rationalize it √(15/x^3) = √(15/x^3) * √x^3/√x^3 = √15 x√x /x^3...
April 12, 2015

Maths help
You posted these before as VINNY. Perhaps if you labeled them as Physics, you might get a tutor to answer them. btw, what does ω=3 2 mean? Is there a missing decimal ? , or ?
April 12, 2015

Physics ??? - Math, Circuits
repost it as physics to get a physics tutor to look at it
April 12, 2015

algebra
I would multiply by 15 to get rid of those fractions, 30d - 5f = 15f - 9d -20f = -39d f = 39/20
April 11, 2015

algebra
so you want: (3/2)x + 1 = (-1/2)x^2 + 2x + 2 times 2 3x + 2 = -x^2 + 4x + 4 x^2 - x - 2 = 0 (x-2)(x+1) = 0 take over
April 11, 2015

algebra
I have this strange feeling you meant: (2a-3)/(a+1) = (3a-5)/(a+3) then 3a^2 -2a - 5 = 2a^2 + 3a - 9 a^2 - 5a + 4 = 0 (a-1)(a-4) = 0 a = 1 or a = 4
April 11, 2015

algebra
let's expand this thing 3x-6y+3x=y-2x-8y 8x = -y 8 = -y/x y/x = -8 y : x = -8 : 1
April 11, 2015

trig
Looks like a straightforward Sine Law problem b/sinB = a/sinA b/sin 60.51° = 3.82/sin 25.25° you do the button pushing
April 11, 2015

alegebra
I noticed that the highest denominator is 2, so let's just double every term ( can't forget to divide by 2 at the end) so we have: 3 8 15 24 35 48 .... the first differences are 5 7 9 11 13 ... and the 2nd differences are 2 2 2 2 ... since the 2nd difference is a ...
April 11, 2015

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

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