# Math Help - πr2 = 21

1. ## πr2 = 21

i have no idea how to solvethis wud sum1 plz help me!

πr2 = 21

pi x r"2" = 21

2. Originally Posted by mezzie
i have no idea how to solvethis wud sum1 plz help me!

πr2 = 21

pi x r"2" = 21
What is the question? Is it rearrange this to something like r= some expression possibly in terms of 21 and pi ...?

Divide both sides by $\pi$ to get:

$r^2=\frac{21}{\pi}$

Now take the sqruare root (we want the positive root because $r$ is presumably the radius of a circle):

$r=\sqrt{\frac{21}{\pi}}$

RonL