Answer:
19.642 cm
Explanation:
f₁ = Focal length of first lens = 11 cm
f₂ = Focal length of second lens = -25 cm
Combined focal length formula
[tex]\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}\\\Rightarrow \frac{1}{f}=\frac{1}{11}+\frac{1}{-25}\\\Rightarrow \frac{1}{f}=\frac{14}{275}\\\Rightarrow f=\frac{275}{14}\\\Rightarrow f=19.642\ cm[/tex]
Combined focal length is 19.642 cm
