已知向量的两个方向余弦分别为，则向量的单位向量为 。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/ddccbadd28ff4393bdbc528098c1dc43.pnghttp://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/7904ae829dab4b16ad7979ea93482956.pnghttp://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/4c2541850dba41bbaf0047a783702fb8.png
举一反三
- 设http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/5f9f81d9a1184c2eb383cb81ebbe2768.png，若http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/410a0d9f8b4a4f82a6818a45f4a3b450.png，http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/637f75734cb849caa773da5377f55f5e.png，http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/29aefd40f6c54e788587a2115dd02467.png，则http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/631634fcf7854ec88eedede14de7c1de.png之间的大小顺序为（ ）<br>
- http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/44f4d22711964c23980340adb7809625.pnghttp://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/3d4966e983de4b688abd5941e42a0548.png
- 空间直线过点，其方向向量是，则直线的对称式方程是 。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/83913f5f8bb349beae5420eb57e94cba.pnghttp://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/c66351c5195f48b29f3ff4fd1e7b4b6d.png
- 设http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/6e6de13adf014e1f9fdc7954cb313377.png是由方程http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/6d1ea7ec74bb4607aee50aa325108197.png确定，求http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/1d60e0ceb7d14d26a00863c192e0bbf3.png（ ）
- 已知http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/4b2b0bc2a81c4059b4ee54fd2d4ca9b8.png，则http://image.zhihuishu.com/zhs/onlineexam/ueditor/201908/1bc083ffe16c4d17a12236cd29409de6.png( )<br>