<p>已知平面<img src="https://file.gaojiufeng.cn/learnAppQuestion/e5/9c/e59c03a91308699bd14a8ae118f4adaf.jpg" style="width: 100%;height: auto;">两两垂直，它们三条交线的公共点为<img src="https://file.gaojiufeng.cn/learnAppQuestion/42/1a/421aeb7d76d192c6843cbc350ddb6a65.jpg" style="width: 100%;height: auto;">过<img src="https://file.gaojiufeng.cn/learnAppQuestion/da/ac/daacc07f6c6e16b222f69ab648b2d289.jpg" style="width: 100%;height: auto;">引一条射线<img src="https://file.gaojiufeng.cn/learnAppQuestion/4b/55/4b551ae705c615a900beb6339de12c73.jpg" style="width: 100%;height: auto;">若<img src="https://file.gaojiufeng.cn/learnAppQuestion/b4/75/b475b8a8ce8750a9f5616f5f56719cd3.jpg" style="width: 100%;height: auto;">与三条交线中的两条所成的角都是<img src="https://file.gaojiufeng.cn/learnAppQuestion/4c/26/4c26abb5e37777cea3b12a6979eacdd6.jpg" style="width: 100%;height: auto;">则<img src="https://file.gaojiufeng.cn/learnAppQuestion/b4/75/b475b8a8ce8750a9f5616f5f56719cd3.jpg" style="width: 100%;height: auto;">与第三条交线所成的角为（）.</p>