Find the coordinates of a point on a circle without knowing the center point.

In summary, to find the coordinates of point B on a circle given point A and other known information such as the radius, slope of the tangent line at A, and length and direction of the arc between A and B, use the fact that the radius at A is perpendicular to the tangent line and the center is located at a known distance along the radius. From there, choose the appropriate location for the center based on the direction of the arc.
  • #1
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Given 2 points on a circle, call them A and B. I know the cartesian coordinates of A. I also know the radius of the circle, the slope of the tangent line at A, and the length and direction of the arc between A and B. I don't know the coordiates of the center of the circle.

How do I find the coordinates of point B?
 
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  • #2
The radius at A is perpendicular to the tangent line. The center is along the radius at a known distance. There are only two possible points. Use the information about B (direction of arc??) to choose the location of the center.
 
  • #3
Thanks mathman. I just needed a little insight, and you have provided that quickly and succinctly.
 

1. How do you find the coordinates of a point on a circle without knowing the center point?

There are two ways to find the coordinates of a point on a circle without knowing the center point. One way is to use the distance formula and the Pythagorean theorem. Another way is to use the equation of a circle: (x - h)^2 + (y - k)^2 = r^2, where (h, k) is the center point and r is the radius.

2. Can you explain the distance formula and the Pythagorean theorem?

The distance formula is used to find the distance between two points on a coordinate plane. It is expressed as d = √((x2 - x1)^2 + (y2 - y1)^2), where (x1, y1) and (x2, y2) are the coordinates of the two points. The Pythagorean theorem states that in a right triangle, the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the other two sides: a^2 + b^2 = c^2.

3. What is the equation of a circle?

The equation of a circle is (x - h)^2 + (y - k)^2 = r^2, where (h, k) is the center point and r is the radius. This equation represents all the points that are equidistant from the center point, creating a perfectly round shape.

4. How do you use the equation of a circle to find the coordinates of a point?

If you know the radius and the center point of a circle, you can plug in those values into the equation (x - h)^2 + (y - k)^2 = r^2 and solve for the coordinates of the point. If you only know the coordinates of the point on the circle, you can plug those values into the equation and solve for the center point and radius first, then use those values to find the coordinates of the point.

5. Are there any other methods to find the coordinates of a point on a circle without knowing the center point?

Yes, there are other methods such as using the slope of the line connecting the center point and the given point on the circle, or using trigonometric functions such as sine and cosine. However, the distance formula and the equation of a circle are the most commonly used methods.

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