方程整理：x1=y²/4 x2=1建立微分：在y=y处,dVy=π（x2²-x1²)dy=π[1²-(y²/4)^2]dy∴Vy=∫【-2,2】{π[1-y^4/16]}dy=2∫【0,2】[π(1-y^4/16)]dy=2π(y-y^5/80)【0,2】=(2*2-2*32/80)π=16π/5
