若a向量的模=1,b向量的模=2,c向量=a向量+b向量,且c向量垂直于a向量,求向量a与b的夹角答案给的是120度 cosQ=a*b/|a|*|b| cosQ=|a|*|b|/2 因为c=a+b,c垂直于a,所以a*(a+b)=0 a`2+a*b=0 a*b=-1cosQ=-1/2 所以夹角=135
来源:学生作业帮助网 编辑:作业帮 时间:2024/09/05 17:34:52
![若a向量的模=1,b向量的模=2,c向量=a向量+b向量,且c向量垂直于a向量,求向量a与b的夹角答案给的是120度 cosQ=a*b/|a|*|b| cosQ=|a|*|b|/2 因为c=a+b,c垂直于a,所以a*(a+b)=0 a`2+a*b=0 a*b=-1cosQ=-1/2 所以夹角=135](/uploads/image/z/8900751-39-1.jpg?t=%E8%8B%A5a%E5%90%91%E9%87%8F%E7%9A%84%E6%A8%A1%3D1%2Cb%E5%90%91%E9%87%8F%E7%9A%84%E6%A8%A1%3D2%2Cc%E5%90%91%E9%87%8F%3Da%E5%90%91%E9%87%8F%2Bb%E5%90%91%E9%87%8F%2C%E4%B8%94c%E5%90%91%E9%87%8F%E5%9E%82%E7%9B%B4%E4%BA%8Ea%E5%90%91%E9%87%8F%2C%E6%B1%82%E5%90%91%E9%87%8Fa%E4%B8%8Eb%E7%9A%84%E5%A4%B9%E8%A7%92%E7%AD%94%E6%A1%88%E7%BB%99%E7%9A%84%E6%98%AF120%E5%BA%A6++cosQ%3Da%2Ab%2F%7Ca%7C%2A%7Cb%7C+cosQ%3D%7Ca%7C%2A%7Cb%7C%2F2++%E5%9B%A0%E4%B8%BAc%3Da%2Bb%2Cc%E5%9E%82%E7%9B%B4%E4%BA%8Ea%2C%E6%89%80%E4%BB%A5a%2A%28a%2Bb%29%3D0++a%602%2Ba%2Ab%3D0++a%2Ab%3D-1cosQ%3D-1%2F2++%E6%89%80%E4%BB%A5%E5%A4%B9%E8%A7%92%3D135)
xRN@.J M:`
ٲ@V@_3SV(֘4{9s_gd)*,r:HoǙ|^y۬nfi}lO>'YfY 9k:NZQE