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若f(sinx)=sin3x,则f(cosx)=?
A.-cos3x
B.cos3x
C.sin3x
D.-sin3x
人气:214 ℃ 时间:2019-12-26 09:21:49
解答
f(cosx)=f[sin(π/2-x)]
=sin[3(π/2-x)]
=sin(3π/2-3x)
=sin[π+(π/2-3x)]
=-sin(π/2-3x)
=-cos3x
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