## Fundamentals of Physics Extended (10th Edition)

$i=-20cm$
Using the lens equation of $$\frac{1}{f}=\frac{1}{p}+\frac{1}{i}$$ solving for $i$ yields $$\frac{p}{pf}-\frac{f}{pf}=\frac{1}{i}$$ $$\frac{p-f}{pf}=\frac{1}{i}$$ $$i=\frac{pf}{p-f}$$ Substituting known values of$f=20cm$ and $p=10cm$ yields $$i=\frac{(10cm)(20cm)}{10cm-20cm}=-20cm$$