【高中数学】已知cosθ=cos30°,则θ等于
cosθ=30
sinθ=0。8或-0。8
cos(θ+30)=sinθcos30+sin30cosθ
=0。8*√3/2+1/2*0。6或-0。8*√3/2+1/2*0。6
=2√3/5+3/10或-2√3/5+3/10
=(4√3+3)/10或(-4√3+3)/10。
cosθ=30
sinθ=0。8或-0。8
cos(θ+30)=sinθcos30+sin30cosθ
=0。8*√3/2+1/2*0。6或-0。8*√3/2+1/2*0。6
=2√3/5+3/10或-2√3/5+3/10
=(4√3+3)/10或(-4√3+3)/10。收起