f(x)=sin(x+7π/4)+cos(x-3π/4)
=sin(x+2π-π/4)+cos(x-π+π/4)
=sin(x-π/4)+cos[-(π-x-π/4)]
=sin(x-π/4)+cos(π-x-π/4)
=sin(x-π/4)-cos(x+π/4)
=sin(x-π/4)-cos(x+π/2-π/4)
=sin(x-π/4)-cos(π/2+x-π/4)
=sin(x-π/4)+sin(x-π/4)
=2sin(x-π/4)
已知函数f(x)=sin(x+7π/4)+cos(x-3π/4)
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