What is the equation for calculating resultant force in Engineering Statics?

[narutoish]

Homework Statement

Homework Equations

F^2 (resultant ) = F1^2 + F2^2 -2F1F2cos(theta)

The Attempt at a Solution

i calculated the magnitude using the equation above and it ended up being :

F (resultant) = F sqrt(2-2cos(theta))

i don't know how to solve for the angle.

 

[Nathanael]

Well in this particular case you can use symmetry (the magnitude of the forces are the same) to find it out.

In general, you could find the angle between two angles by solving for $\phi$ in this equation: $\vec a\cdot \vec b=|a||b|cos\phi$
(Of course, you would want to use some coordinate system to find $\vec a\cdot \vec b$)

 

[narutoish]

So in this case we say it's theta/2?

 

[Nathanael]

So in this case we say it's theta/2?

Yep