# Lenses Question

by Grekory
Tags: lenses
 P: 2 When i'm given do, ho, and hi. How would i solve for di Normally i would do -di/do = hi/ho and cross-multiply but i'm not sure how the negative comes into effect. do = object distance di = image distance ho = object height hi = image height If... ho = 3cm hi = 4cm do = 5cm What would be di? Thanks
 Mentor P: 40,264 Please provide the complete statement of the problem you are trying to solve. (I presume that a negative image height means that the image is inverted.)
 P: 2 It's just made up values and i want to know how i would solve for di. The negative in the formula confuses me
Mentor
P: 40,264

## Lenses Question

Start with:
-di/do = hi/ho

You can solve for di by cross-multiplying if you like, or just multiply both sides by -do. As I said before, a negative value for di just means that the image is inverted. (Real images are inverted.)

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