已知a=(3,-4),b=(2,3),则2|a|-3a•b=_.
问题描述:
已知
=(3,-4),a
=(2,3),则2|b
|-3a
•a
=______. b
答
∵
=(3,−4)a
∴|
|=a
=5
32+(−4)2
•a
=3×2−4×3=−6b
∴2|
|−3a
•a
=28b
故答案为28.