解sin(派＋a)=-½即-sin(a)=-½即sin(a)=½即cosα=√3/2或cosα=-√3/2sin(二分之派＋a)+cos(a-二分之三派)=cosα-cos（二分之三派-α）=cosα+sinα即cosα+sinα=√3/2+1/2或cosα+sinα=-√3/2+1/2
