The parabola y = AX2 + BX is tangent to the straight line x + y in the first quadrant. The area of the figure enclosed by the parabola and the X axis is s. find Smax

The parabola y = AX2 + BX is tangent to the straight line x + y in the first quadrant. The area of the figure enclosed by the parabola and the X axis is s. find Smax

The parabola and the straight line are tangent in the first quadrant. The linear equation cannot be x + y = 0. Is it a clerical error? It should be x = y
If it is not x + y, it can only be x + y = C > 0; let's consider it x = y for the moment
If the first quadrant is tangent, there must be a