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# Interpreting expressions with multiple variables: Cylinder

Given the vale and the expression for the radius of a cylinder, find the radius of a cylinder with the same volume and 100 times the height. This involves analyzing the expression for the radius to see how changing the height affects the radius. Created by Sal Khan.

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• I like to try solving these problems before I watch the video. I solved this question a little differently as a result.
I rearranged the given equation to solve for V, as both cylinders shared the same volume. I put the 20m radius on one side and the 100h on the other, then solved for r.

r = sqrt(V/h(pi)) : V = h(pi)r^2
r^2(pi)100h = h(pi)(20)^2

Thankfully I still got the same answer.
• 1/3A-Bsquared
If I increase b the expression becomes more negative but also if I decrease b won’t the same thing happen be cause of the negative in front of the b because anything squared is positive