I looked and beheld a man with a measuring stick in his hand..
Zacharia 2:1

Its extremely difficult and dangerous to corectly align the mirror facets in a segmented solar reflector. Before starting construction, an array builder needs to know the formulas needed to get the mirrors at the proper angle to illuminate the receiver. Here's some basic geometry and trig that shows you how to do it.

Step 1: Linear Optics

The angle of incidence equals the angle of reflection. The rest is Euclidean plane geometry from high school. Dust off those old books....
....and you always wondered why they taught you that stuff!

Step 2: Plug and Crank

Its just high school trig and some algebra, rememeber that old Greek guy Euclid?

Two equations in two unknowns, solve it and use it as a spreadsheet formula.

The PDF file explains the math and gives you the formula: