速求!1.已知sin(30＋α)＝3／5.60＜α＜150.求cosα 2.已知tanα,tanβ是方程2X＋3x－7＝

sin(30＋α)＝3／5 .60＜α＜150 cos(a+30)=-4/5
cosα=cos[(a+30)-30]=cos(a+30)cos30+sin(a+30)sin30
=-4/5*√3/2+3/5*1/2
=(3-4√3)/10
tana+tanb=-3/2
tana*tanb=-7/2
tan(a+b)=(tana+tanb)/(1-tana*tanb)
=(-3/2)/(1+7/2)
=-1/3