Hi Kevin,
If you square the two equations you get
2 = 0.25 cos^{2} A + cos^{2} B + cos A cos B
0.25 = 0.25 sin^{2} A + sin^{2} B  sin A sin B
Now add the two equations and simplify using the fact that sin^{2} X + cos^{2} X = 1.
Do you now see a trig identity that helps?
Penny
