二次函数等角问题方法总结
1）利用等角的tan值求解
https://www.bilibili.com/video/BV1du411p7Ma
https://www.bilibili.com/video/BV1Kh411F7rg
2）等角“加上/减去”同角或等角
https://www.bilibili.com/video/BV1Vk4y1s7QX
https://www.bilibili.com/video/BV1HX4y1a7AV
https://www.bilibili.com/video/BV1yo4y1M7oM
3）构造相似三角形
https://www.bilibili.com/video/BV1Ac41137Yp
https://www.bilibili.com/video/BV1Fc41137sQ
https://www.bilibili.com/video/BV1rm4y1i7RK
4）其他方法（平行 、 等腰 、 等弧对等角）
https://www.bilibili.com/video/BV1ks4y1e7eS
https://www.bilibili.com/video/BV1M8411Z7RK
https://www.bilibili.com/video/BV1Th4y1V7hG
5）构造三垂直
a.固定顶点
https://www.bilibili.com/video/BV1Hm4y1i78V
(原题： https://www.bilibili.com/video/BV1yo4y1M7oM）
https://www.bilibili.com/video/BV1Zo4y1u7cN
(原题： https://www.bilibili.com/video/BV1HX4y1a7AV)
https://www.bilibili.com/video/BV1Bu4y1Z7kZ
(原题： https://www.bilibili.com/video/BV1du411p7Ma)
b.移动顶点
https://www.bilibili.com/video/BV1yW4y1X74n
（原题： https://www.bilibili.com/video/BV1rm4y1i7RK)
https://www.bilibili.com/video/BV17P411Q7zG
（原题： https://www.bilibili.com/video/BV1Fc41137sQ)
