Question

已知平面向量a和b满足,|a|=1,|b|=2,且a与b的夹角为120°,则|2a+b|等于?

Answer 1

|2a+b|^2 = (2a+b).(2a+b) = 4|a|^2+|b|^2 + 4|a||b|cos120°=4+4-4 =4

|2a+b|=2