[总结反思] 对于sin α+cos α,sin α-cos α,sin αcos α这三个式子,利用(sin α±cos α)2=1±2sin αcos α可以达到转换、知一求二的目的.
应用演练
1.【微点1】[2018·南昌模拟] 已知sin θ=1/3,θ∈(π/2 "," π),则tan θ= ( )
A.-2 B.-√2
C.-√2/2 D.-√2/4
2.【微点1】已知tan x=-12/5,x∈(π/2 "," π),则cos-x+3π/2= ( )
A.5/13 B.-5/13
C.12/13 D.-12/13
3.【微点2】[2018·遵义模拟] 若点(2,tan θ)在直线y=2x-1上,则sinθcosθ/(1"-" sin^2 θ)= ( )
A.2 B.3
C.4 D.6
4.【微点3】若sin θ,cos θ是方程4x2+2mx+m=0的两根,则m的值为 .
第18讲 同角三角函数的基本关系式与诱导公式