How far apart are an object and an image formed by a 75.0cm focal length converging lens if the

Question

image is 2.5x larger than the object and is real.
Please, help me.

Answer 1

Use two equations to get di and do. First, 1/f=1/do+1/di (textbooks usually use p and q).

Also, M = -di/do.

Since the image is real, di is positive and M is negative (image is upside down). Using the second equation, -2.5 = -di/do. Solving for di, di=2.5*do.

We can substitute this into first equation to get, 1/75 = 1/do + 1/(2.5*do). Solving for do, do = 105.

Now we put this into either equation, for example, 1/75 = 1/105 + 1/di and solve for di: di = 262.5

So finally, di + do = 105 + 262.5 = 367.5 cm