# Math Help - kindly help me for this proof of triangles

1. ## kindly help me for this proof of triangles

the question and figure is attached

2. Hi

You need to use the fact that angle $\theta$ is unchanged at reflection

Using Pythagorean theorem

$l = \sqrt{(h_t-h_r)^2+d^2}$

$x + x' = \sqrt{(h_t+h_r)^2+d^2}$