Answer
$i=-100\pm 100\sqrt{\frac{A}{P}}$
Work Step by Step
$A=P(1+\displaystyle \frac{i}{100})^{2}$
Divide by P:
$\frac{A}{P}=(1+\frac{i}{100})^{2}$
Square root both sides: $\pm\sqrt{\frac{A}{P}}=1+\frac{i}{100}$
Subtract 1:
$-1\pm\sqrt{\frac{A}{P}}=\frac{i}{100}$
Solve for $i$:
$i=-100\pm 100\sqrt{\frac{A}{P}}$
