# Homework Help: Geometry problem

1. Dec 21, 2011

### SoggyBottoms

1. The problem statement, all variables and given/known data
Disparity is defined as $\delta = \alpha - \beta$. Find $\delta$ in terms of interocular distance a, viewing distance D and d, e and f.

http://img220.imageshack.us/img220/7576/43519392.jpg [Broken]

3. The attempt at a solution

I'm not getting anywhere. Any tips to get me started?

Last edited by a moderator: May 5, 2017
2. Dec 21, 2011

### bbbeard

I would start by writing down the tangent relations. For example, α is the difference between the two angles that Q and P make from the vertical (forward?) direction. So

α = atan(f/(D+d)) - atan(e/D)

and so forth.

BBB

3. Dec 22, 2011

### SoggyBottoms

Thanks. Then:

$\beta = \arctan(\frac{a - e}{D}) - \arctan(\frac{a - f}{D + d})$