Question

已知a^2+b^2=1,x^2+y^2=1,a,b,x,y∈R,用向量方法证明：-1≤ax+by≤1

Answer 1

楼上,题目变了!

= = = = = = =

以下u,v表示向量（要加箭头）.

证明：令 u=(a,b),v=(x,y),则

|u|=a^2+b^2=1,

|v|=x^2+y^2=1.

u.v=ax+by.

所以 cos=u.v/(|u||v|)

=ax+by.

又因为 -1