已知向量a,b满足| a |=1 b=(2,1)且λ a+b=0 则 |λ |=
问题描述:
已知向量a,b满足| a |=1 b=(2,1)且λ a+b=0 则 |λ |=
答
设a=(x,y)x^2+y^2=1入x+2=0 入y+1=0
=> 入=-2/x=-1/y =>4y^2+y^2=1=>y=±√5/5
∴ λ=±√5 =>|λ|=√5