设 C,B∈ C.Cl a,为一组基 =XC1+x2C2+…+xn B=yax1+y2a2+…+ynan 于是 a+B=(x1+n1)a1+(x2+y2)a2+…+(xn+yn)Cn ka=ha+h,a,.+h,a设 ,   Vn 1 2 , , , ,   n 为一组基 1 1 2 2 n n     = + + + x x x 1 1 2 2 n n     = + + + y y y 于是 1 1 1 2 2 2 ( ) ( ) ( ) n n n      + = + + + + + + x y x y x y 1 1 2 2 n n k kx kx kx     = + + +