1v+1u=1f\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}v1+u1=f1
m=uv\mathrm{m}=\dfrac{u}{v}m=vu
p=1f\rm{p}=\dfrac{1}{f}p=f1
1f=1f1+1f2+…\dfrac{1}{f}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}}+\dotsf1=f11+f21+…