a|=√a,a (a,B) p=arccos 0<≤兀 D aB a⊥B=(a,B)=0 1 Cauchy- Schwarz不等式,(a,P)≤|af 设a a+…+aO√ 2 2 C1+…+a +…+b rbf(x)g(x)dx< raf(x)dx ra2(x)cx3 ( , ) arccos , 0        =   1.Cauchy − Schwarz不等式，（，）   .    = ( , ), ( , ) 0. D     ⊥ = = 设   ， 则       =         = n bn b a a   1 1  ,  2 2 2 2 1 1 1 1 n n n n a b a b a a b b + +  + + + + 2 2 ( ) ( ) ( ) ( ) b b b a a a    f x g x dx f x dx g x dx 