ek='=n咖北== F0=1=+号+ 2=0+2,(连续倒 Ew-n=R-aF=z D(X)=EX2)-IE(X)=1/2. 网国☒( ) ( ) [ ( )] / . ( ) ; ( ) / ; . ( ) arcsin ,( ) ( ) arcsin | 1 2 1 2 1 0 1 2 1 1 1 2 1 2 1 1 1 1 1 1 2 2 1 1 2 2 2 1 1 2 1 1 1 1 2 = − = = − = = − =        = =         = + = +  = + = = = = − =     − − + − − − D X E X E X dx x x dx E X x x E X a b F a a a dx b x b x b f x dx        连续性