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View Full Version : How to solve for variable are


guria1
Aug 20, 2009, 10:06 AM
I don't get how to solve this math problem:
I have to solve for r>0
A=2pie*(r squared) + s=2pie*r*h

when I take everything over to the other side, I have r + r squared left on one side. Now I don't get how to combine r and r squared. Please help!!

Unknown008
Aug 20, 2009, 10:15 AM
Firstly, \pi is pi, not pie as in apple pie.

I think you're speaking of the formula for the total surface area of a cylinder, right? Then, don't put is the way you did, since it causes confusion. Also, your question is also confusing in the way that you want to solve for r>0. If r>0, then A>0. But if you want to make r the subject of formula, then that's something else.

A = 2\pi r^2 + S

S = 2 \pi rh

A= 2\pi r^2 + 2\pi rh = 2\pi (r^2 + rh)

\frac{A}{2 \pi}= (r^2 + rh)

You cannot go any further if you don't have any more information. If it was given for example, the height h = 2r, then, you can go on.