一.平面区域D的面积 =』do=J rare D D ex1计算y=a2及x+y=3a(a>0用围成图形的面积 Solution 5a 2a) 2 jdo=a』 D (2a 2 5∠x 2 15 Ddx =(-2In 2)a 8 K心一 .平面区域D的面积 =  D  d =  D rdrd ( 0) . 2 5 1. ex 计算xy = a 2及x + y = a a  围成图形的面积 Solution. x y o ) 2 (2 , a a ,2 ) 2 ( a a =  D  d =  a a dx 2 2  −x a x a 2 dy 5 2 =  − − a a dx x a x 2 a 2 2 ) 2 5 ( 2ln2) . 8 15 ( 2 = − a