Y=-X^2-3X+3，X+Y=-X^2-2X+3当X=-1时，X+Y有最大值4
X+Y=3-X2-2X 极值点为X=-1 带入得X+Y<=4
x方+3x+y-3=0所以x+y=-x方-2x+3 =-(x方+2x-3) =-(x+3)(x-1)画出等式右边的抛物线，可以得知抛物线的最大值是0
