已知a=(3,-4),b=(2,3),则2|a|-3a•b=_.

问题描述:

已知

a
=(3,-4),
b
=(2,3),则2|
a
|-3
a
b
=______.

a
=(3,−4)
|
a
|=
32+(−4)2
=5
a
b
=3×2−4×3=−6

2|
a
|−3
a
b
=28

故答案为28.