名校
1 . (1)证明“直线与平面垂直的判定定理”:如果一条直线与一个平面内的两条相交直线垂直,则该直线与此平面垂直.
已知:如图,
,
,
,
.求证:
;
![](https://img.xkw.com/dksih/QBM/2023/11/17/3369796464435200/3370169716801536/STEM/653a2bc095e040b2a0c772ff8704c289.png?resizew=130)
(2)证明:平行四边形两条对角线的平方和等于两条邻边的平方和的两倍.
如图,四边形
是平行四边形.求证:
.
已知:如图,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6182bd53bccdad13334835221362a4d2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60750b5eab6344496e925eb603cab46a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff290c28b42c8380283f6259daaec5c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac16b6d9ffc65507c5cd4083a1363937.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e380108ba2cf04e68a5a9393d2b921c.png)
![](https://img.xkw.com/dksih/QBM/2023/11/17/3369796464435200/3370169716801536/STEM/653a2bc095e040b2a0c772ff8704c289.png?resizew=130)
(2)证明:平行四边形两条对角线的平方和等于两条邻边的平方和的两倍.
如图,四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7105465941e9c130703b15790c6c1ecf.png)
![](https://img.xkw.com/dksih/QBM/2023/11/17/3369796464435200/3370169716801536/STEM/35d2213ed5264d45abd83c78d2631c9a.png?resizew=141)
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