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

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??

Answers and Replies

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.

D H
Staff Emeritus
Science Advisor
Read chriscolose's answer. Is 191.05 between -180 and +180?

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.

D H
Staff Emeritus
Science Advisor
A good start is to draw a picture. What does that tell you?

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.

D H
Staff Emeritus
Science Advisor
What trigonometric formulae do you think need to be used to solve this problem?

Our job here is to help you do your own homework; we do not do your homework for you.

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.

Soh cah toa

sin=opposite/hyp.
cos=adjacent/hyp
tan=opposite/adjacent

D H
Staff Emeritus
Science Advisor
Then maybe your drawing should have a triangle that you can make sense of rather than an arc that you cannot make sense of.