Question

请各位学霸帮忙，需要过程，谢谢！

Answer 1

① 当k为奇数时，令k=1
则原式=sin(π－a)cos((1-1)π－a)／sin((1+1)π＋a)cos(π+a)
=sin(a)cos(－a)／sin(2π＋a)(－cos(a))
=sin(a)cos(a)／sin(a)(－cos(a))
=-1

追答

②当k为偶数时，令k=0
则原式=sin(－a)cos(-π-a)/sin(π+a)cos(a)
=(－sin(a))(cos(－(π+a)))/(sin(－a))cos(a)
=(－sin(a))cos(π+a)/(-sin(a))cos(a)
=-cos(a)/cos(a)
=-1
∴原式=-1