# Vectors physics homework -- Addition of two vector forces

Homework Statement
Two forces.. F and 2F..the angle between them is x prove that their resultant is R=root square(1+8cos^2 x/2) X F
Homework Equations
R=root square(1+8cos^2 x/2) X F
Trying to solve it

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#### berkeman

Mentor
Welcome to the PF.

Your attachment is sideways and pretty hard to read. Can you please type your work into the forum? That makes it a lot easier to respond.

There are math symbols in the Edit bar above the edit window under the √ symbol, and there is a tutorial about how to use LaTeX under the Help pages (see INFO at the top of the page). Thanks.

#### BvU

Homework Helper

My neck still hurts from trying to read your picture ( I use a desktop, not a phone). For the sake of others I re-post it:

I notice your x is not the $x$ in the exercise (which is your $\theta$# ) so that deciphering isn't just painful, but also confusing.
As @berkeman (who types faster) says: could you re-post and explain what it is you write down?

In the mean time you can try to find a relevant equation that links $\cos\theta$ and $\cos(\theta/2)$ and post that too

Oh, and: read this

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