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# Stuck on a maths vector question. watch

1. https://i.gyazo.com/6e4c7e83c8014155...5e2f28eb58.png
This is the question I'm stuck on, I've got part a done but it's mainly part b that I cant do, I just don't really know where to begin. Any help would be appreciated.
2. (Original post by Relentas)
https://i.gyazo.com/6e4c7e83c8014155...5e2f28eb58.png
This is the question I'm stuck on, I've got part a done but it's mainly part b that I cant do, I just don't really know where to begin. Any help would be appreciated.
Just dot the two vectors since its asking for a dot product.

Take the two vectors, and expand the brackets
3. (Original post by RDKGames)
Just dot the two vectors since its asking for a dot product.

Take the two vectors, and expand the brackets
Surely that just gives 2a^2 + 2b^2

OM = a + 2b
OL = 2a + b
4. (Original post by Relentas)
Surely that just gives 2a^2 + 2b^2

OM = a + 2b
OL = 2a + b
Erm.. no

(a+2b).(2a+b) = 2a.a + 5a.b + 2b.b

Then just use the fact that a.a = magnitude(a)^2
5. (Original post by RDKGames)
Erm.. no

(a+2b).(2a+b) = 2a.a + 5a.b + 2b.b

Then just use the fact that a.a = magnitude(a)^2
Ohh, I was treating a and b as actual units rather than vectors, this helped a lot, thanks!

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