A x2J(16+x2) x(25+y2) ∞16+x 25+ 5 a n T 4=20 451 (25 ) 1 (16 ) 1 2 2 2 = +  +    −  − dy y dx x A  即 1 20 4 5 25 5 1 , 16 4 1 2 2 2   =  = = + = +    −  − A A dy y dx x      