【急】已知函数f(x)=sinxcosx-√3sin^2x+√3/2已知a b 属于(0,π/2) f(a/2-π/6)=3/5 f(b/2+π/12)=12/13 求cos(a+b)
问题描述:
【急】已知函数f(x)=sinxcosx-√3sin^2x+√3/2
已知a b 属于(0,π/2) f(a/2-π/6)=3/5 f(b/2+π/12)=12/13 求cos(a+b)
答
f(x)=sinxcosx-√3sin^2x+√3/2
=1/2*sin2x-√3/2*(1-cos2x)+√3/2
=1/2*sin2x+√3/2*cos2x)
=sin(2x+π/3)
f(a/2-π/6)=sina=3/5,
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