数学将函数平移后可以问题
2009-12-04 10:10:57l***
数学将函数平移后可以问题数学将函数平移后可以问题：y =f(x)sinx
按向量a =(π/4,0)平移后,得
f(x -π/4)sin(x -π/4)
2(sinx)^2 ?
最佳回答
y =f(x)sinx
按向量a =(π/4,0)平移后,得
f(x -π/4)sin(x -π/4)
2(sinx)^2 -1
=(sinx)^2 -(cosx)^2
= (sinx +cosx)(sinx -cosx)
=2sin(x +π/4)sin(x -π/4)
=[2cos(x -π/4)]sin(x -π/4)]
f(x -π/4)=2cos(x -π/4)
从而
f(x)=2cosx
所以选C
2009-12-04 11:29:46
倒回去。将y=2(sinx)^2-1=-cos2x平移（-π/4，0）得
y=-cos2(x+π/4)=sin2x=2cosxsinx,
f(x)=2cosx.
2009-12-04 11:25:54
很赞哦！ (116)
