Calculating Forces in x-y Plane on 5.60 kg Mass

[alfredo24pr]

Homework Statement

Three forces in the x-y plane act on a 5.60 kg mass: 9.90 N directed at 17o, 7.40 N directed at 167o, and 3.80 N directed at 208o. All angles are measured from the positive x-axis, with positive angles in the Counter-Clockwise direction. Calculate the magnitude of the acceleration. Calculate the direction of the resultant force using the same sign convention as above (in degrees).

Homework Equations

*I do not have problem with the magnitude of acceleration, just the angle!*

tan 0 = y/x

The Attempt at a Solution

x component results in - 1.1
y component results in 2.77

the angle has to be expressed from the positive x axis, when i solve tan inverse(2.77/-1.1)
I get -68.3 degrees, therefore from positive x-axis it equals 291.7 degrees. The LONCAPA (an internet homework place, marks my answer incorrectly). Did I do something wrong?

 

[PhaseShifter]

tan (angle)=tan(angle+180º)

 

[alfredo24pr]

tan (angle)=tan(angle+180º)

thats it! Thank you :D