若sin^2α-sin2α-3cos^2α=0,则tanα=?
问题描述:
若sin^2α-sin2α-3cos^2α=0,则tanα=?
答
sin^2α-sin2α-3cos^2α=0
sin^2α-2sinαcosα-3cos^2α=0
两边同时除以cos^2α,得:
tan^2α-2tanα-3=0
(tanα+1)(tanα-3)=0
tanα=-1或3