Location of object on axis of concave mirror?

[jlmccart03]

Homework Statement

Where on the axis of a concave mirror would you place an object to get a half-size image? Express the object distance in terms of the focal length f. Follow the sign convention.

Homework Equations

(1/q)+(1/p)=(1/f)
f=(2/R)

The Attempt at a Solution

I attempted to use the object distance plus image distance to solve for f (I just got f=q+p), but the online homework system says that is wrong. Are these the correct formulas and what should I be doing?

 

[Merlin3189]

Those equations don'tmention image size. So you need an idea about that, or maybe an equation.
Have you drawn a diagram?

 

[jlmccart03]

Those equations don'tmention image size. So you need an idea about that, or maybe an equation.
Have you drawn a diagram?

But they do? I wrote them differently, but it's (1/D_o)+(1/D_i)=(1/f)

EDIT: wait I misread that. You are talking about (H'/H)=(f/k)

 

[Merlin3189]

Yes. I don't recognise the formula you give (H'/H)=(f/k) ?
But it's the ratio of heights (H'/H) that matters. You know what number this is, from the question.
How do the heights relate to the distances ? (That's where I thought a diagram might help.)

 

[Merlin3189]