Hi Kevin,
If you square the two equations you get
2 = 0.25 cos2 A + cos2 B + cos A cos B
0.25 = 0.25 sin2 A + sin2 B - sin A sin B
Now add the two equations and simplify using the fact that sin2 X + cos2 X = 1.
Do you now see a trig identity that helps?
Penny
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