已知角α终边上一点P(-4,3),求cos(5π/2+α)sin(-π+2α）/cos(11π/2-α)sin（9π/2+α）的值.
问题描述：
已知角α终边上一点P(-4,3),求cos(5π/2+α)sin(-π+2α）/cos(11π/2-α)sin（9π/2+α）的值.
前面是5π/2!好多题是π/2.
答
角α终边上一点P(-4,3),则：sinα=3/5,cosα=-4/5
原式=sinαsin2α/(-sinαcosα)
=-2sinα
=-6/5