y=3+2x-x^2=0
解得x=3,x=-1
化为定积分
∫[1,3](3+2x-x^2)dx-∫[3,5](3+2x-x^2)dx
=(3x+x^2-x^3/3)[1,3]-(3x+x^2-x^3/3)[3,5]
=2*(9+9-9)-3-1+1/3-15-25+125/3
=16
面积=积分(1-->3)(3+2x-x^2)dx+积分(3-->5)(x^2-2x-3)dx
=(3x+x^2-x^3/3),[1->3]+(x^3/3-x^2-3x),[3-->5]
=(9+9-9)-(3+1-1/3)+(125/3-25-15)-(9-9-9)
=16