Question

convex lens of power 4d and a concave lens of power 3d are placed in contact what is the equivalent power of the combination​

Answer 1

Convex lens has positive focal length and diverge lens have negitive focal length power will be... 1/4-1/3= -1/12

Answer 2

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P=P1+P2

P1=+4D(convex)

P2=-3D(concave)

P=4D-3D=1D