答案是π/2y在[-0.25~0]之间,设给定一个y,对应的圆环面积s为: π( (X1)^2-(X2)^2 ) = π(X1-X2)(X1+X2)上式中X1,X2为 X^2-3X+2-y=0的两个根( (3 + (1+4y) ^0.5)/2, (3 -(1+4y) ^0.5)/2 )s = 对( 3π((1+4y) ^0.5) dy )的积分 (y在[-0.25~0]之间)积分结果为π/2