It is known that the parabola y = AX2 + BX is tangent to the straight line x + y = 4 in the first quadrant. The area of the figure enclosed by the parabola and the x-axis is denoted as S. find the A and b values that make s reach the maximum value, and find the maximum value of S

It is known that the parabola y = AX2 + BX is tangent to the straight line x + y = 4 in the first quadrant. The area of the figure enclosed by the parabola and the x-axis is denoted as S. find the A and b values that make s reach the maximum value, and find the maximum value of S

The abscissa of the intersection of parabola and x-axis is X1 = 0, X2 = - BA, so s = ∫ - BA0 (AX2 + BX) DX = (13ax3 + 12bx2) | - BA0 = 13a · (- BA) 3 + 12b · (- BA) 2 = 16a2 · B3 (1) The linear x + y = 4 is tangent to the parabola y = AX2 + BX