Question

Prove that for a combination of two thin coaxial lenses of focal lengths $F_{1} and F_{2}$, seperated by distance x, the focal length of combination is given by equation $\frac{1}{F} =\frac{1} f_{1}}+\frac{1}{f_{2}}-\frac{x}{f_{1}f_{2}}$

Answer 1

hence prove this question