Can someone me on an equilibrium problem?

[darlingdarlin]

i have my physics exam tomorrow and i need help understanding this problem because i got this wrong on a previous test

Homework Statement

Two concurrent forces are acting on a box with a mass of 50.0 kg. One force is 555 N acting at an angle of 140 degrees; the other force is 785 N at an angle of 200 degrees. What third force would have to be added to the situation to produce a state of equilibrium?

Homework Equations

f= ma i guess... i didnt use it though

The Attempt at a Solution

555sin(40)-785sin(20) >> V
-555cos(40)-785cos(20) >> H
then i square rooted V^2 + H^2
then i tan^-1(V/H)
and i got some negative funky number

 

[mtayab1994]

Use the principle of deficiencies.

 

[darlingdarlin]

Use the principle of deficiencies.

what is that?

 

[mtayab1994]

$$\sum(F)=0$$

 

[darlingdarlin]

$$\sum(F)=0$$

i probably sound really stupid saying this but.. is that calculus? because if it is i am currently only in algebra II

 

[mtayab1994]

i probably sound really stupid saying this but.. is that calculus? because if it is i am currently only in algebra II

No that's not calculus that sign (sigma) stands for the sum of all forces.

 

[darlingdarlin]

No that's not calculus that sign (sigma) stands for the sum of all forces.

okay thank you!
i really appreciate it

 

[mtayab1994]

okay thank you!
i really appreciate it

Did you learn how to use the principle of inertia?