# 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◦).

## 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??

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

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
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
What trigonometric formulae do you think need to be used to solve this problem?

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.