Question: A man is looking at the top of a tower. The angle of elevation to the top of the tower is 10 degrees. 100m closer to the tower, a man has an angle of elevation to the top of the tower of 20 degrees, how tall is the tower? My Problem: I can solve this ver easily by recognizing that an isosceles triangle is formed when you draw the line of sight of the closer man, and since one of the sides of the isosceles is 100m the other side is as well, then I solve the smaller right triangle with tangents and get an answer approximately equal to 36m. But, this unit is on Cosine law, and I don't see how I can solve this with cosine law. Help?