解
P(-4m,3m)
r=|OP|=5|m|.
sina=y/r=(3m)/(5|m|)
cosa=x/r=(-4m)/(5|m|)
∴原式
=[6m/(5|m|)]+[-4m/(5|m|)]
=2m/(5|m|)
当m＜0时,原式=-2/5
当m＞0时,原式=2/5
∴原式=±2/5