(cosx)^8 =[( cosx)^2]^4 = (1/16) (1 + cos2x)^4 = (1/16) [ (1 + cos2x)^2 ]^2=(1/16) [ 1 + 2 cos2x +( cos2x)^2 ]^2 = (1/4) [ 3/2 + 2 cos2x + ...
確定! 回上一頁