Solve for di: Negative Effect on Object Distance?

[Grekory]

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

 

[Doc Al]

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.)

 

[Grekory]

It's just made up values and i want to know how i would solve for di. The negative in the formula confuses me

 

[Doc Al]

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.)