Deriving the Thin Lens Formula: How Does Equation 1 Relate to the Triangles?

[Larrytsai]

Hi I need help on figuring where and how 1/f = 1/do + 1/di
My teacher told me it relates to the ray diagram but i have no clue where to start to find where this formula has come from. Any help would be much appreciated.

 

[rock.freak667]

Here shows you how to derive it.

 

[Larrytsai]

Here shows you how to derive it.

WOW thank you so much... i can't even explain how happy uve made me. I know this will help for sure but could you explain about how equation 1 relates to the triangles to me please. Just make it a lil more clearer to me:D or could someone explain to me how
di/f -1 is related to
Ab/cd = Af/df like i see the labels on the diagram but it doesn't make sense like why we divide f and stuff sry if u guys can't understand what I am trying to say