1.a+tb=(-3+2t,2+t),(a+tb)^=(-3+2t)^+(2+t)^=9-12t+4t^+4+4t+t^=5t^-8t+13=5(t-4/5)^+9.8,当t=4/5时（a+tb)^最小，|a+tb|最小.2.a-tb=(-3-2t,2-t)与c共线，<==>(-3-2t)/3=(2-t)/(-1),<==>3+2t=6-3t,<==>5t=3,t=3/5.
