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burhan101
 one year ago
Solve for r
burhan101
 one year ago
Solve for r

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burhan101
 one year ago
Best ResponseYou've already chosen the best response.0\[\large 0=\frac{ r2700 }{ r^2 }+62 \pi r\]

calculusxy
 one year ago
Best ResponseYou've already chosen the best response.0You are trying to find the area of a radius?

calculusxy
 one year ago
Best ResponseYou've already chosen the best response.0Sorry I meant the area of a circle.

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0No it's an optimization problem I am trying to do, I just need to solve for 'r'

calculusxy
 one year ago
Best ResponseYou've already chosen the best response.0Oh I thought that because the formula to finding the area of a circle,you have to first square the radius and then multiply it by pi (r^2)3.14.

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Multiply everything by r^2. Then factor out an r. From there it's a quadratic.

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Oh my bad. You actually get a cubic.

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0top and bottom or just top?

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Multiply everything by r^2. When you multiply the fraction, multiply on top.

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0\[r^2 or \frac{ r^2 }{ r^2 }\]

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0yeah so woulnt that cancel out with the fraction

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Yes =) That's the point. It gets r out of the denominator.

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0ohh i thought you were also telling me to muktiply the top by r^3 so the function would be diff, i misunderstood

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1\(\huge 0 = \frac{r2700}{r^2} + 62\pi*r\) multiply everything by r^2 \(\huge (0)*r^2 = (\frac{r2700}{r^2})*r^2 + (62\pi*r)*r^2\)

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Gives: \(\huge 0 = r2700 + 62\pi*r^3\)

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1And honestly from there your best bet is to use a cubic solver of some sort. Wolfram Alpha should do just fine.

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0dw:1371520632051:dw yeah but the thing is like during an exam i cant use it :P

Bad2zBone
 one year ago
Best ResponseYou've already chosen the best response.0Are you sure the question is correct?

Bad2zBone
 one year ago
Best ResponseYou've already chosen the best response.0I suggest you double check, because you will not solve this without the aid of wolfaplha

burhan101
 one year ago
Best ResponseYou've already chosen the best response.0here is the question and my solution

Bad2zBone
 one year ago
Best ResponseYou've already chosen the best response.0I suggest you take a look at this http://gbbservices.com/math/cubic.html

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Okay on the step where you take C', you make incorrect use of the quotient rule. The derivative of the top will be 0.

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1The correct derivative is: \(\Large C' = \frac{27900}{r^2} + 62\pi*r\)

SmoothMath
 one year ago
Best ResponseYou've already chosen the best response.1Set the derivative equal to 0 and solve: \(\Large \frac{27900}{r^2} + 62\pi*r = 0\) \(\Large (\frac{27900}{r^2} + 62\pi*r)*r^2 = 0*r^2\) \(\Large 27900 + 62\pi*r^3 = 0\) \(\Large 62\pi*r^3 = 27900\) You good from there?
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