# Math Help - Dot Product Problem

1. ## Dot Product Problem

Assume that , , and . What is the value of ?

Please help!

2. Originally Posted by Del
Assume that , , and . What is the value of ?

Please help!
From $|\vec u| = 3$ you know that $\vec u \cdot \vec u = 9$

Now expand the given term:

$7 \vec u \left(4 \vec u - 3 \vec v \right) = 28 \vec u \cdot \vec u - 21 \vec u \cdot \vec v = 28 \cdot 9 - 21 \cdot 3 = 189$