For a 35mm camera, the equation 1/f = 1/di + 1/do represents the focal length (f) of the lens that is needed to produce a clear photograph. ?

Question

Can someone explain to me the step by step on how to solve this? This question genuinely has me stumped.

Answer 1

Hints: Unanon yourself and we will further help you. 

Can you type in the question? It would help of for copy/paste so we can answer you.  

From 1/f = 1/di + 1/de, thus 1/de = 1/f - 1/di, right?

Now replace di & f by the given functions. Done!

Simplify if need be. 

Answer 2

1/do = 1/f - 1/di

= (x^2 + x - 2)/(x^2 - 9) - (2x^2 + 10)/(x^2 + 2x - 3)

= (x^2 + x - 2)(x-1)/[(x+3)(x-3)(x-1)] minus

(2x^2 + 10)(x - 3)/[(x+3)(x-3)(x-1)]

= (x^3 - 3x + 2 - 2x^3 + 6x^2 - 10x + 30) / [(x+3)(x-3)(x-1)]

= (32 - 13x + 6x^2 - x^3)/[(x+3)(x-3)(x-1)]

Answer 3

Are you that lazy. Some guy answered this last night.