为你守望2000
幼苗
共回答了17个问题采纳率:70.6% 举报
f(x)=cos^2(x/2)-sin(x/2)cos(x/2)-1/2
=1/2(1+cosx)-1/2sinx-1/2---注:∵cos2x=2cos^2(x)-1∴2cos^2(x/2)=1+cosx∴cos^2(x/2)=1/2(1+cosx).∵sinx=2sin(x/2)cos(x/2)∴sin(x/2)cos(x/2)=1/2sinx
=1/2+1/2cosx-1/2sinx-1/2
=1/2(cosx-sinx)
=1/2*根号2(根号2/2*cosx-根号2/2*sinx)
=根号2/2*(cosπ/4*cosx-sinπ/4*sinx)
=根号2/2*cos(x+π/4)----------------------注:cos(a+b)=cosacosb-sinasin
1年前
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