Math quirk, how to come up with this?

[chaser0]

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The lens makers formula is

1/f=1/o+1/i

And br derives the equation

I=(o•f)/(o-f)

How did they get that equation?? I always end up with

I=(f•o)/(f-o)

Because you are

1/f-1/o=1/i

 

[milski]

You are skipping a minus sign somewhere?

1/f=1/o+1/i |*foi
o*i=f*i+f*o
o*i-f*i=f*o
i(o-f)=f*o
i=f*o/(o-f)

 

[chaser0]

I am not missing a minus sign though

Why is my way wrong?
Because they come out with completely different answers.

 

[chaser0]

Oh wait, i think i know why

Nvm

 

[milski]

I am not missing a minus sign though

Why is my way wrong?
Because they come out with completely different answers.

Can't tell without seeing what you're doing. 😉

 

[Morsetlis]

The lensmaker's formula is: Never give the patient their PD, lest they go buy their glasses from Hong Kong or India.

 

[dmf2682]

E k says we don't need to memorize that one?