As shown in the image:
There are two right triangles:
the triangle are similar
naming the points for easy calculation
measure of the angle zyw = measure of the angle yxw
And the measure of the angle ywz = measure of the angle xwy
So, the triangle WYZ will be similar to the triangle WXY
So, the corresponding side will be in proportion
In the right triangle ywz:
using Pythagorean theorem: