证明:记=P(x)P(x)tx I (l-x2)p(m (x). pom)(x)cr -x)y0(x)p( 出(小2(xp( ((-x)()女证明： ( ) ( ) 1 , -1 m m m l k l k 记I = ò P x P x dx ( ) ( ) ( ) ( ) ( ) 1 2 -1 -1 1- m m m l k d x P x P x dx dx = ò ( ) ( ) ( ) ( ) ( ) 1 -1 2 -1 - 1- m m m k l d P x x P x dx dx é ù ò ê ú ë û ( ) ( ) ( ) ( ) ( ) 1 2 -1 -1 1- m m m l k = x P x P x ( ) ( ) ( ) ( ) ( ) 1 -1 2 -1 - 1- m m m k d P x x P x dx dx l é ù = ò ê ú ë û