trig
posted by marie on .
1) Use doubleangle identities to write the following expression, using trigonometric functions of x instead of 4x.
cos 4x
2) Use halfangle identities to write the following expression, using trigonometric functions of x instead of x/4.
sin x/4

cos4x = 2cos^2(2x)1
= 2(2cos^2(x)1)^2  1
just expand that
sin(x/4) = sqrt((1cos(x/2))/2)
= sqrt((1sqrt((1cos(x))/2)/2