要利用到的公式：cos2a=cosa-sina=cosa-(1-cosa)=2cosa-1 则cosa=1/2+1/2cos2a f(x)=cosx/2-sinx/2cosx/2-1/2 =1/2cosx+1/2-1/2sinx-1/2 =1/2cosx-1/2sinx =√2/2(√2cosx-√2/2sinx) =√2/2(cosx*cosπ/4-sinπ/4*s...