SOLUTION: If sin 2A = cos 12B, find tan (A + 6B)?

sin(2A) = cos(12B)

cos(90°-2A) = cos(12B)

cos(90°-2A) - cos(12B) = 0

We use the identity:  

 with x=90°-2A and y=12B



Divide both sides by -2 and simplify the angles





Use zero-factor property:

Since we are only interested in A+6B we set only the second
factor = 0



Use the identity  to make (A+6B) positive:



Divide both sides by -1 and reverse the terms









Edwin