Question

两个向量相加的模怎么计算?向量a,b夹角60° |a|=5.|b|=8 则 |a+

Answer 1

a*b=|a||b|cos=20

|a+b|^2=a^2+2a*b+b^2=25+40+64=129

|a+b|=根号下129