dot product question (1 Viewer)

[kractus]

Just not sure where to start. I wrote out equations where i let a and b be some arbitrary vector and got nowhere.

 

[jimmysmith560]

Would the following working help?

 

[wizzkids]

If you are struggling to get started with vector questions, then try drawing a diagram of what is going on.

From the definition of the dot product, we know that 5=a x b x cosΘ
With those hints, can you finish it off?