sin(π-α)-cos(π+α)=根号2/4(0

sin(π-α)-cos(π+α)=根号2/4(0
sin(π-α)-cos(π+α)=根号2/4(0

sin(π-α)-cos(π+α)=根号2/4(0
因为　sin（π－α）＝sinα 　cos（π＋α）＝－cosα
所以原式=sinα+ cosα=根号二/4
则（sinα+ cosα）^2=1/8 即1+2sinαcosα=1/8
所以2sinαcosα=-7/8 由此得出2/π