Question

Sinx的四次方＋cos四次方＝九分之五 求sin2x

Answer 1

(sinx)^4+2(sinx)^2(cosx)^2+(cosx)^4=1 2(sinx)^2(cosx)^2=4/9 (sinx)^2(cosx)^2=2/9 sinxcosx=±√2/3 2sinxcos=±2√2/3 sin2x