1) Find the exact value of cos 105 degrees by using a half-angle formula. 2)Find the solution of sin 2theta = cos theta if 0 degrees/= theta 180...

1) Find the exact value of cos 105 degrees by using a half-angle formula.2)Find the solution of sin 2theta = cos theta if 0 degrees</= theta < 180 degrees.I have read the book and looked at the examples, but cannot figure out how to work these. Any help would be great!!Thanks