Question

一道数学题目~向量

Answer 1

因为整天都是向量,所以略去向量二字
AP*BC=(BP-BA)(BA+AC)=(BM/3-BA)(BA+AC)=(BA/3+AM/3-BA)(BA+AC)
=(AM/3-2BA/3)(BA+AC)=(2AC/9-2BA/3)(BA+AC)
=2AC*BA/9+2AC^2/9-2BA^2/3-2BA*AC/3
=2AC^2/9-2BA^2/3-4AC*BA/9
=2-8/3+4AB*AC/9
=4|AB||AC|cos120°/9-2/3=4*2*3*(-1/2)/9-2/3=-2

Answer 2

因为整天都是向量,所以略去向量二字
AP*BC=(BP-BA)(BA+AC)=(BM/3-BA)(BA+AC)=(BA/3+AM/3-BA)(BA+AC)
=(AM/3-2BA/3)(BA+AC)=(2AC/9-2BA/3)(BA+AC)
=2AC*BA/9+2AC^2/9-2BA^2/3-2BA*AC/3
=2AC^2/9-2BA^2/3-4AC*BA/9
=2-8/3+4AB*AC/9
=4|AB||AC|cos120°/9-2/3=4*2*3*(-1/2)/9-2/3=-2
楼上的别抄我的！

Answer 3

因为整天都是向量,所以略去向量二字
AP*BC=(BP-BA)(BA+AC)=(BM/3-BA)(BA+AC)=(BA/3+AM/3-BA)(BA+AC)
=(AM/3-2BA/3)(BA+AC)=(2AC/9-2BA/3)(BA+AC)
=2AC^2/9-2BA^2/3-4AC*BA/9
=2-8/3+4AB*AC/9
=4|AB||AC|cos120°/9-2/3=4*2*3*(-1/2)/9-2/3=-2
楼上的2位别抄我的！ !!!!!