Vector Calculus Multi

[atse1]

Hello,

I have a math problem I kept trying but it doesnt seem to be going anywhere.

The problem asks:

What is the angle between a and b if

\(\displaystyle a \cdot b = -|a| |b|\)

If anyone can point me in the direction to get started correctly, I am most thankful.


So far, I've tried substituting a and b with numbers where a=<3,4> and b=<5,12> but that doesn't seem to take me anywhere. :[.

 

[mmm4444bot]

Hi atse1:

\(\displaystyle a\) and \(\displaystyle b\) are vectors and \(\displaystyle a \cdot b\) is their dot product, right?

If so, you should find the following (geometric) definition of the dot product very useful.

\(\displaystyle a \cdot b \;=\; |a| \:\: |b| \;\; cos(\theta)\)

Cheers ~ Mark