# Cartesian plane distances

1. Jun 10, 2013

### Robertoalva

1. The cartesian coordinates of a point in the xy plane are x=−9.92 m, y=−2.8 m.Find the distance "r" from the point to the origin.Answer in units of m

2. Relevant equations

A=sqrt(Axi^2 + Ayj^2)

3. The attempt at a solution

i did the following:
A=sqrt((-9.92m)^2 + (-2.8m)^2) and got for answer 10.30m

is that right?

2. Jun 10, 2013

### Robertoalva

also, there's this second part, where I'm stuck.

Calculate the angle θ 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 degrees

3. Jun 10, 2013

### lewando

Your "r" looks right. Have you tried drawing a picture of the situation?

4. Jun 10, 2013

### Robertoalva

for the second one? yes, the point lies in the third quadrant, now the thing is how to get the angle, there's an equation tantheta= y/x, I did it and i got tantheta= .28 which if i want to get the angle,i just have to get tan^-1 right?

5. Jun 10, 2013

### lewando

That will give you an angle which will be helpful in determining the answer, but it is not the answer.

6. Jun 10, 2013

### Robertoalva

hmmm, okay, then what do you suggest would be the next step then? do I subtract that angle from another one?

7. Jun 10, 2013

### lewando

First, what did you get for your arctan(.28)?
Second, are you clear about how they want you to report the answer "measured counterclockwise from the positive x axis, within the limits of −180◦to +180◦"

8. Jun 10, 2013

### Robertoalva

i got 15.64 degrees and no! that part messes me up, i think the limit me, only to the 0 to the 180 (first and second quadrant)

9. Jun 10, 2013

### lewando

Is it 0 to 180 (makes no sense)? Or -180 to 180 (makes sense).