# Cosine and Sine rules to get magnitude and direction of a resultant force

1. Oct 20, 2009

### baylayA

Use the cosine and sine rules to determine the magnitude and direction of the resultant of a force of 11 kN acting at an angle of 50 degrees to the horizontal and a force of 6 kN acting at an angle of -30 degrees to the horizontal.

2. Oct 20, 2009

### danago

What have you tried doing? Have you drawn a diagram of the situation -- Will make things much easier.

3. Oct 20, 2009

### baylayA

No i haven't.
Do you know how to find resultant forces with forces and angles from axises? because I have another problem like that and i have no idea how to do them

4. Oct 20, 2009

### danago

Well maybe draw one then At least then you actually have a triangle to apply the cosine and sine rules to.

If you are given forces and angles relative to axes, you could again do the same thing and form a triangle to be solved with geometry, or perhaps easier would be to resolve each force into a horizontal and vertical component and add the components.

5. Oct 9, 2010

### haaaaa87

Hi All
to get magnitude of resultant use cosin rule R^2= X^2+Y^2 – 2XYcosβ
to get the direction use sine rule = (Sin β /length of opposite line) = (sinθ/ length of opposite line)