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第1个回答 2018-11-25
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第2个回答 2018-11-25
6、sin(3π+α)=sin(2π+π+α)
=sin(π+α)=-sinα=-1/2
则cos(7π/2 - α)=cos(2π + 3π/2 - α)
=cos(3π/2 - α)=-sinα
=-1/2
8、对称轴是2x - π/3=kπ + π/2
2x=kπ + 5π/6
∴x=kπ/2 + 5π/12，(k∈Z)
9、sin(π/4 - α)=sin(π/2 - π/4 - α)
=sin[π/2 - (α + π/4)]=cos(α + π/4)
=2/3追答
=sin(π+α)=-sinα=-1/2
则cos(7π/2 - α)=cos(2π + 3π/2 - α)
=cos(3π/2 - α)=-sinα
=-1/2
8、对称轴是2x - π/3=kπ + π/2
2x=kπ + 5π/6
∴x=kπ/2 + 5π/12，(k∈Z)
9、sin(π/4 - α)=sin(π/2 - π/4 - α)
=sin[π/2 - (α + π/4)]=cos(α + π/4)
=2/3追答
10、∵cos2x=1 - 2sin²x
∴f(sinx)=3 - 2(1 - 2sin²x)
=3 - 2 + 4sin²x=4sin²x + 1
则f(x)=4x² + 1
∴f(cos15º)=4cos²15º + 1
=2•2cos²15º + 1
=2(1 + cos30º) + 1
=2(1 + √3/2) + 1
=2 + √3 + 1
=3 + √3
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