What are the polar coordinates of (1,-2) and how do you find them?

In summary, the conversation discusses converting the point (1,-2) to polar coordinates and finding two representations, one with r > 0 and one with r < 0. The equations used are tantheta = y/x and x^2 + y^2 = r^2. The result obtained is (sqrt(5), arctan(-2)) and (-sqrt(5), arctan(-2) + pi). It is questioned whether arctan(-2) satisfies 0 <= theta <= 2 pi and it is determined that adding 360 to -63.43° would satisfy the interval.
  • #1
Jbreezy
582
0

Homework Statement



Convert (1,-2) to polar coordinates find one representation with r >0 and one with r <0. Also 0<= theta <= 2 PI

Homework Equations



I used tantheta = y /x , and x^2 +y^2 = r^2

The Attempt at a Solution



I got (sqrt(5) , arctan(-2)) , (-sqrt(5) , arctan(-2) + pi )
Is this OK?
 
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  • #2
Does arctan(-2) satisfy 0 <= theta <= 2 pi?
 
  • #3
I think so it is -63.43 degrees in my calculator and I forget how arctan comes back in the calculator but if I add 180 to that it is still only 116. I forget where is comes back to the domain on the calculator I mean.
 
  • #4
But -63.43° is not in the interval [0°, 360°]. That was essentially what SteamKing was objecting to.
 
  • #5
OH opps. OK so add 360 to it. Then I'm good right?
 

Related to What are the polar coordinates of (1,-2) and how do you find them?

1. What are polar coordinates?

Polar coordinates are a two-dimensional coordinate system that represents a point in a plane using a distance from the origin and an angle from a reference line.

2. How do you convert between polar and Cartesian coordinates?

To convert from polar to Cartesian coordinates, use the formulas x = r * cos(theta) and y = r * sin(theta), where r represents the distance from the origin and theta represents the angle from the reference line. To convert from Cartesian to polar coordinates, use the formulas r = sqrt(x^2 + y^2) and theta = arctan(y/x).

3. What is the purpose of polar coordinates?

Polar coordinates are useful for representing points in a circular or radial pattern, such as in physics, engineering, and astronomy. They are also helpful in describing complex shapes and curves.

4. How do you plot points in polar coordinates?

To plot a point in polar coordinates, start at the origin and move a distance of r units along the reference line, then rotate an angle of theta degrees in the direction specified. The point where the distance and angle intersect is the plotted point.

5. What is the difference between polar and rectangular coordinates?

The main difference between polar and rectangular coordinates is the way they represent points in a plane. Rectangular coordinates use x and y values to indicate a point's position along the horizontal and vertical axes, while polar coordinates use a distance and angle from the origin. Additionally, polar coordinates are better suited for representing circular or radial patterns, while rectangular coordinates are better for linear patterns.

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