converging lens

Question

A converging lens and a diverging lens are placed 12 cm from each other. Where will this combination of lenses produce an image of a distant object if the converging lens has a focal length of 20 cm and the diverging lens a focal length of –6 cm?

Answer 1

Image in 1st lens located at f = F₁ = 20 cm. Thes for second lense we have d₂ = - (20 - 12) = - 8 cm and by formul 1/F₂ = 1/d₂ + 1/f₂; - 1/6 = - 1/8 + 1/f₂; f₂ = - 24 cm. So, image we have in front of second lenz in 24 cm from it