1.|a+b|=根号下[(a+b)^2]
=根号下(a^2+2ab+b^2)
=根号下(|a|^2+2|a||b|cos60+|b|^2)
=根号下(1+2*1*1*1/2+1)
=根号下3
2.(a+nb)(3a-b)=0
3a^2-ab+3nab-nb^2=0
3-1+3n-n=0
n=-1