f=0,2 m=20 cm
C=1/f=1/0,2=5 δ
1/f=1/x₂-1/x₁=>x₂=fx₁/(f+x₁)=20(-10)/(20-10)=-200/10=-20 cm->imagine virtuala
d=|x₁|+|x₂|=|-10|+|-20|=10+20=30 cm
|x₁'|=20+|x₁|=20+10=30 cm
1/f=1/x₂'-1/x₁'=>x₂'=fx₁'/(f+x₁')=20(-30)/(20-30)=-600/(-10)=60 cm
β=x₂'/x₁'=60/(-30)=-2