Question

若x=π/12.则sinx^4-cosx^4=?sinx^4+cosx^4=?

Answer 1

sinx^4-cosx^4=(sinx^2-cosx^2)(sinx^2+cosx^2)=sinx^2-cosx^2=-cos2x=-√3/2

sinx^4+cosx^4=(sinx^2+cosx^2)^2-4sinx^2 *cosx^2=1-(sin2x)^2=3/4