化简数列c1+c2+c3.+cn1,2,3,n是代表数列的第几个cos2x=0.6,则cos^4x+sin^4x=?_数学解答

化简数列c1+c2+c3.+cn
1,2,3,n是代表数列的第几个
cos2x=0.6,则cos^4x+sin^4x=?

人气：268 ℃　时间：2020-09-30 21:27:33

解答

cos^4x+sin^4x
=cos^4x+sin^4x+2*cos^2xsin^2x-2*cos^2xsin^2x
=(sin^2x+cos^2)^2-2*cos^2xsin^2x
=1-2*(1-sin^2x)*sin^2x
=1-2*(1-(1-cos2x)/2)*(1-cos2x)/2
=1-2*(1-0.2)*0.2
=1-.32
=0.68