Question 650021
Find r such that pir^2 = 2pir

{{{pi * r^2 = 2*pi*r}}}
Divide both sides by pi

{{{r^2 = 2r}}}
{{{r^2-2r = 0}}}
{{{r(r-2) = 0}}}
r= 0 or r=2

r=2 is the only non-zero number that fits the bill.

2.