已知函数f(x)=ax^3+bx^2+cx在点x0处取得的极大值是5，其导函数y=f(x)的图像经过(1,0)(2,0)，如图所示

f(x) = ax^3 + bx^2 + cx f'(x) = 3ax^2 + 2bx + c, 0 = f'(1) = 3a + 2b + c, ...(1) 0 = f'(2) = 12a + 4b + c. ...(2) 因方程有2个不同的根，所以 a 不等于0. 0 = 9a + 2b, 2b = -9a. f''(x) = 6ax + 2b f''(1) = 6a + 2b = 6a - 9a = -3a,