Solving Equations

Wow CPhill, taking the easy route are ye?

Since 15 degrees is in both, we can let that equal A

So what we have after substituting A for 15 degrees is 

cos²A - sin²A

That equals Cos2A

So we can substitute 15 degrees for A

So we get cos2(15)

Cos30

The cos of 30 degrees is 

pi/6

So all solutions to this are pi/6 +2(pi)(N) where N is any real integer

This isn't as tough as it looks, Shades.....

Note .....A = 15°

So

Cos (2A)  =

Cos (2 *15)  =

Cos(30)  =

√3 / 2

Wow... okay I think I need some sleep or coffee or both. Thanks so much!