已知2sinθ-cosθ=0 试求1)sin2θ的值 2)(sinθ)^2+sinθcosθ的值
问题描述:
已知2sinθ-cosθ=0 试求1)sin2θ的值 2)(sinθ)^2+sinθcosθ的值
答
2sinθ=cosθ
(sinθ)^2+4(sinθ)^2=1
(sinθ)^2=1/5
sin2θ=2sinθcosθ=2sinθ*2sinθ=4*1/5=4/5
(sinθ)^2+sinθcosθ=1/5+1/2*4/5=3/5