[\sqrt{A_1A_2}] A lens is placed between a source of light and a wall. It forms images of area A1 and A2 onthe w

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A lens is placed between a source of light and a wall. It forms images of area A1 and A2 on
the wall, for its two different positions. The are of the source obtained is

$\frac{(A_1 + A_2)}{2}$

$\sqrt{A_1A_2}$

$[a^{-1}_{1} + a^{-1}_{2}]^{-1}$

$[\frac{\sqrt{A_1}+\sqrt{A_2}}{2}]^2$

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