Question

向量a,b满足a的绝对值=2,b的绝对值=3,且a,b夹角大小为π/3,求a*b的值 并且求a-b的绝对值

Answer 1

a*b=|a|*|b|*cos(π/3)=2*3*1/2=3

|a-b|^2=a^2-2a*b+b^2

=4-2*3+9

=7

所以|a-b|=√7