If the line y = x is the tangent of the curve y = x3-3x2 + ax, then a=______ .

If the line y = x is the tangent of the curve y = x3-3x2 + ax, then a=______ .

Let the tangent point P (x0, x0) ∵ the straight line y = x be the tangent of the curve y = x3-3x2 + ax ∵ the slope of the tangent is 1 ∵ y = x3-3x2 + ax ∵ y ′ x = x0 = 3x2-6x + a ∵ x = x0 = 3x02-6x0 + a = 1 ∵ the point P is on the curve ∵ x03-3x02 + ax0 = x0 ∵ from ① and ②, x0 = 03x20 − 6x0 + a − 1 = 0 ③ or X20 − 3x0