sin（24π/5）
=sin(4π+4π/5)
=sin(4π/5)
=sin(π-π/5)
=sin(π/5)
cos（-17π/4）
=cos(17π/4)
=cos(4π+π/4)
=cos(π/4)
=cos(π/2-π/4)
=sin(π/4)
∵π/2>π/4>π/5
∴sin(π/4)>sin(π/5)
∴
cos（-17π/4）>sin（24π/5）
cos（24π/5）
=cos(5π-π/5) ∵5π在x负轴上 ∴5π-π/5在第二象限
=-cos(π/5)
cos（-17π/4）
=cos(17π/4)
=cos(4π+π/4)
=cos(π/4)
∵π/5