Calc Angle b/w Radius Vector Point & +x Axis: What Does That Mean?

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tngo1206
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Calc. Angle between radius vector point and positive x axis? What does that mean?

Homework Statement



The cartesian coordinates of a point in the xy
plane are x = −8.96 m, y = −1.75 m.

Calculate the angle  between the radius-
vector of the point and the positive x axis
(measured counterclockwise from the positive
x axis, within the limits of −180◦ to +180◦).
Answer in units of ◦.

Homework Equations



arctan of (y/x) = angle/degree



The Attempt at a Solution



I did arctan of y/x = 11.051 incorrect...
I did the arctan of y/x + 180 and got 191.05 incorrect...
I did that same method - 180 = 168 ish still inccorrect...
then I did arctan of x/y + 180= 258 ish and still wrong..

any ideas what this question is asking for? or what the correct answer is??
 
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191.05 looks right but not within the limits of what they want. Try to express that another way.
 
I have this exact same problem with different numbers! (UT homework maybe? XD) I'm pretty stuck.
 
Here is my problem:

The cartesian coordinates of a point in the xy plane are x = −8.83 m, y = −5.47 m. The distance between the point and the origin is 10.38700149. Calculate the angle  between the radius-vector of the point and the positive x-axis (measured counterclockwise from the positive x axis, within the limits of −180◦ to +180◦). Answer in units of ◦.

I have no idea how he got his answer at all.
 
Okay, I drew a picture and I have a graph with a circle. I have the radius as 10.38700149 and I drew an arc (representing the angle) from the the positive x-axis counterclockwise to the radius in the third quadrant.
 
I understand that. XD That's why I asked. I wasn't expecting anyone to do anything for me. :3

Anyway, hmm, what formula? I can't say that I know. I mean, I'm thinking it has something to do with sin, but I'm not entirely sure.
 
sin=opposite/hyp.
cos=adjacent/hyp
tan=opposite/adjacent