sinA+sin^2A=1,cos^2A+cos^6A=?
问题描述：
sinA+sin^2A=1,cos^2A+cos^6A=?
答
sinA+sin^2A=1=sin^2A+cos^2A
所以：sinA=cos^2A
cos^2A+cos^6A
=sinA+sin^3A
=sinA+sinA(1-sinA)
=sinA+sinA-(sinA)^2
=2sinA-sin^2A
=2sinA-(1-sinA)
=3sinA-1
答
设sina=tt+t^2=1t^2+t-1=0delta=1+4=5t1=-1+√5/2t2=-1-√5/2(舍)sina=√5-1/2cos^2A+cos^6A =sinA+sin^3A =sinA+sinA(1-sinA) =sinA+sinA-(sinA)^2 =2sinA-sin^2A =2sinA-(1-sinA) =3sinA-1=3*√5-1/2-1=3√5-5/2...