已知tana=3,则sin²a-3sinacosa+cos²a的值=
问题描述:
已知tana=3,则sin²a-3sinacosa+cos²a的值=
答
sin^2a-3sinacosa+cos^2a
=(sin^2a-3sinacosa+cos^2a)/(sin^2a+cos^2a)
=(tan^2a-3tana+1)/(tan^2a+1)
=(3^2-3*3+1)/(3^2+1)
=1/10