Well, take the derivative first, and then put forward six, because the image is about negative semi-symmetry. . . When the quadratic function is transformed into the form of (X-M)*2+N, we know that m here is negative half. You see, he put forward 6, leaving a clean quadratic equation. The quadratic term coefficient is 1, which should be x*2+a/3x-2, but since we know that M above is negative half, A/3 =. . The core of this wonderful solution lies in that ingenious idea. You will understand it after reading more. Thanks for your hard work, hope to adopt it.