student 12th grade
Can one derive a triple angle formula for sine and cosine? If so, how?
sin 3x = 3sin x - 4(sin3x)
There are many easy ways, but since you probably know the formulas for the sine and cosine of 2x and of a+b, just use those formulas on 3x = 2x + x:
cos 3x = 4(cos x)3 - 3cos x.
Go to Math Central