题目

In Yangzhou, a morning tea experience has a complete set of accompanying rules that needs to be observed. In fact, it is a miniature Formal banquet because it includes a variety of food, ranging from cold dishes to various dim sum, staple food, fruits, and seasoning dishes.【1】 and the delicacies are served slowly one after another. The variety of dishes and dim sum as well as the preparations reflect the laid-back lifestyle of Yangzhou locals.Tea, of course, is an essential part of every morning tea.【2】. With a soft taste, the green tea is what makes the whole experience. It helps clea如图，在Rt△ABC中，∠BAC＝90°，AB＝4，AC＝3，点D，E分别是AB，AC的中点，点G，F在BC边上(均不与端点重合)，DG∥EF.将△BDG绕点D顺时针旋转180°，将△CEF绕点E逆时针旋转180°，拼成四边形MGFN，则四边形MGFN周长l的取值范围是___________. ≤l＜13 【解析】如图,连接DE,作AH⊥BC于H. 在Rt△ABC中, ∵∠BAC=90°AB＝4，AC＝3，, , , , , , , , , ∴四边形DGEF是平行四边形, , 根据题意,, ∴四边形MNFG是平行四边形, ∴当MG=NF=AH时,可得四边形MNFG周长的最小值= , ...