Question 32481
COS(4X)=COS(2(2X))=COS^2(2X)-SIN^2(2X)
={COS^2(X)-SIN^2(X)}^2-{2SIN(X)COS(X)}^2
=COS^4(X)+SIN^4(X)-2COS^2(X)SIN^2(X)-4SIN^2(X)COS^2(X)
=COS^4(X)-6COS^2(X)SIN^2(X)+SIN^4(X)