Question

Solve for r

Answer 1

\[\large 0=\frac{ r-2700 }{ r^2 }+62 \pi r\]

Answer 2

You are trying to find the area of a radius?

Answer 3

Sorry I meant the area of a circle.

Answer 4

No it's an optimization problem I am trying to do, I just need to solve for 'r'

Answer 5

Oh 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.

Answer 6

Multiply everything by r^2. Then factor out an r. From there it's a quadratic.

Answer 7

Oh my bad. You actually get a cubic.

Answer 8

top and bottom or just top?

Answer 9

Multiply everything by r^2. When you multiply the fraction, multiply on top.

Answer 10

\[r^2 or \frac{ r^2 }{ r^2 }\]

Answer 11

Just r^2

Answer 12

yeah so woulnt that cancel out with the fraction

Answer 13

Yes =) That's the point. It gets r out of the denominator.

Answer 14

ohh i thought you were also telling me to muktiply the top by r^3 so the function would be diff, i misunderstood

Answer 15

\(\huge 0 = \frac{r-2700}{r^2} + 62\pi*r\)
multiply everything by r^2
\(\huge (0)*r^2 = (\frac{r-2700}{r^2})*r^2 + (62\pi*r)*r^2\)

Answer 16

Gives:
\(\huge 0 = r-2700 + 62\pi*r^3\)

Answer 17

And honestly from there your best bet is to use a cubic solver of some sort. Wolfram Alpha should do just fine.

Answer 18

yeah but the thing is like during an exam i cant use it :P