用拉格朗日乘子法求带约束最大化问题：构造拉格朗日函数f(x, y, l) = x + λy + l (x2+y2+xy-1)令f对x和y的偏导数为0,得：1 + 2lx+ly = 0; λ+ 2ly + lx=0;解方程组得：x = (-2+l)/(3l), y = (-2+λ)/(3l)代入不等式...