只讲解第四个问题，并生成视频---Here is the extracted content from the image: **Overall Context:** (2023秋·岳麓区校级期末) 压轴题 --- **Question (1)** * **Question Stem:** 已知x, y, z为△ABC的三边长，且有 (√x + √y + √z)^2 = 3(√xy + √xz + √yz) . 试判断△ABC的形状并加以证明。 * **Mathematical Formulas/Equations:** (√x + √y + √z)^2 = 3(√xy + √xz + √yz) --- **Question (2)** * **Question Stem:** 已知x, y满足xy+3y-x-10=0, 且x,y都是整数, 求x的值. * **Mathematical Formulas/Equations:** xy+3y-x-10=0 --- **Question (3)** * **Question Stem:** 在平面直角坐标系中，已知点A (0, 3) , B (-4, 0) , 在y轴上求一点C, 使得△ABC是等腰三角形，求C点的坐标。(画图，在图上标出坐标) * **Key Data Points:** A (0, 3), B (-4, 0) --- **Question (4)** * **Question Stem:** 如图，在四边形ABCD中，∠BAD=∠BCD=90°, ∠ABC=135°, AB=3√2, BC=1, 在AD、CD上分别找一点E、F, 使得△BEF的周长最小，求△BEF周长的最小值. * **Mathematical Information:** ∠BAD=90°, ∠BCD=90°, ∠ABC=135°, AB=3√2, BC=1. * **Chart/Diagram Description:** * **Type:** Geometric figure (Quadrilateral). * **Main Elements:** * **Points:** Four vertices labeled A, B, C, D. * **Lines:** Straight line segments connect the vertices to form a quadrilateral ABCD. * **Relative Position:** * Point A is at the top-left. * Point B is below and to the left of A. * Point C is below B, and slightly to its right. * Point D is to the right of C, and slightly below the horizontal level of A. * The side AB appears longer than BC. * **Angles:** The angle at vertex A (∠BAD) and the angle at vertex C (∠BCD) are depicted as right angles. The angle at vertex B (∠ABC) is depicted as an obtuse angle. * **Labels:** Vertices are labeled A, B, C, D. The problem specifies points E on AD and F on CD, though E and F are not explicitly marked on the provided diagram.