double angle/half angle formulas
I have two problems for homework tonight that I can't get.
they are over double and half angles.
if someone can get any of these, and show how they did it or give a short explanation how, that would be awesome.
1. sin2x[4cos^4(x) - 4cos^2(x)]^2
I started by changing sin2x to 2sinxcosx & squared the parenthetical part
then I multiplied it all out but I don't see any way to simplify.
2. sin(C + D) = 7/8, (C+D) is in quadrant I, and sin C = 2/8, C is in quadrant I
find sin D
this one I'm rather lost. I know the formula for sin(C + D), so I can make it
(sinC)(cosD) + (cosC)(sinD) = 7/8
change the sin C to 2/8... but can't get it all figured out.