
已知函数f(x)=cos²[(π/4)+ x] - cos²[(π/4)- x]。则f(π/12)等于( )
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f(x)=cos²(π/4+x)—cos²(π/4—x)
=cos²(π/4+x)—sin²(π/4+x)
=cos2(π/4+x)=cos(π/2+2x)
= -sin2x
f(π/12)= -sinπ/6= -1/2
=cos²(π/4+x)—sin²(π/4+x)
=cos2(π/4+x)=cos(π/2+2x)
= -sin2x
f(π/12)= -sinπ/6= -1/2
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