请用一元二次方程的思路解答这道题---**Heading:** 核心考点一 利用配方法求面积最值 **Question 01:** 如图, 四边形 ABCD 的两条对角线 AC, BD 互相垂直, AC+BD=12, 当 AC, BD 的长分别是多少时, 四边形 ABCD 的面积最大? 解： **Image Description:** The image shows a quadrilateral labeled ABCD. The vertices are labeled A, B, C, and D in counterclockwise order, starting from the bottom left. The two diagonals, AC and BD, are drawn inside the quadrilateral. The diagonals intersect at a point. A small square symbol is shown at the intersection point, indicating that the diagonals AC and BD are perpendicular to each other. There are no coordinate axes, scales, or units shown.