Hi everyone, I have a really hard triangle of forces diagram can anyone help me?

I have a hard question which I just cant do can anyone help me?

Triangle of froces.
figures: 1) 5N at 15degrees to above west of the horizontal.
2) 7N at 20degrees to the above west of the horizontal
3) unknown force?

question A) To show that coplanar forces acting on an object in equilibrium graphically by a triangle of forces.
B) To solve analytically the same force system as in (A) above.


Please may someone teach me this if you have any visual representations then send them to mini_elliso@hotmail.co.uk

Thans everyone

Answers:
Well probably the easiest way is to draw a triangle. Draw two lines, both going from the same point, one of length 5, 15degrees above horizontal, another of length 7, 20degrees above the horizontal, then find the angle and the length of the line that joins them up. It doesn't matter what units the lengths are in, but just to make it easier you could make them 5cm and 7cm. This will show you visually what the situation looks like. Then you can the cosine rule to find the final force (i.e. the length of the third line), and basic trigonometry to find the angle.
do your homework yourself
try looking at www.mathsnet.net and under mechanics section
woo that is a tricky one.
The unknown force acts at 17.9 degrees below east of the horizontal, and it is 11.99 Newtons in force.

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