Question

向量a,b,c满足a+b+c=0且a垂直b,绝对值a=1,绝对值b=2,则绝对值c的平方等于?

Answer 1

|c|^2=|-a-b|^2=|a+b|^2=|a|^2+|b|^2+2ab=1^2+2^2+2*0=5