Question
Make $R_2$ the subject of formula $R^2=4 \pi\left(R_1{ }^2-R_2{ }^2\right)$
✓
Answer
$R^2=4 \pi\left(R_1^2-R_2^2\right) $
$ \Rightarrow R^2=4 \pi R_1^2-4 \pi R_2^2$
$ \Rightarrow 4 \pi R_2^2=4 \pi R_1^2-R^2$
$ \Rightarrow R_2^2=\frac{4 \pi R_1^2-R^2}{4 \pi}$
$ \Rightarrow R_2=\sqrt{\frac{4 \pi R_1^2-R^2}{4 \pi}}$
$ \Rightarrow R^2=4 \pi R_1^2-4 \pi R_2^2$
$ \Rightarrow 4 \pi R_2^2=4 \pi R_1^2-R^2$
$ \Rightarrow R_2^2=\frac{4 \pi R_1^2-R^2}{4 \pi}$
$ \Rightarrow R_2=\sqrt{\frac{4 \pi R_1^2-R^2}{4 \pi}}$
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