问题:
已知| | =" 6," 与 的夹角为60 0, ( + 2 )·( -3 ) = -72, 则| |为
A.5
B.16
C.5
D.4
已知| | =" 6," 与 的夹角为60 0, ( + 2 )·( -3 ) = -72, 则| |为
A.5 | B.16 | C.5 | D.4 |
参考答案: