Question

已知向量a=3e1-2e2,b=4e1+e2,其中e1=（1,0）,e2=（0,1） 求：（1）a*b;\a+b/; （

Answer 1

(1)

a*b = (3e1-2e2)(4e1+e2) = 12e1^2 - 5e1e2 - 2e2^2 = 12*1 - 5*0 - 2*1 = 5

|a+b| = |(3,-2) + (4,1)| = |(7,-1)| = √50

(2)cos = a*b/(|a|*|b|) = 5/(√13*√17) = 5√221/221