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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
 

Attachments

berkeman

Mentor
55,704
5,790
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. :smile:
 

BvU

Science Advisor
Homework Helper
12,318
2,740
Hello Ahmad, :welcome: !

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:
1567439733353.png

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:frown:) 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 :smile:

Oh, and: read this
 
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