Question 117909This question is from textbook Algebra and Trigonometry (Sullivan)
: I need to find the general form of the equation of a circle. The problem in the book is "find center at the point (-3,1) and tangent to the y-axis. Im taking a correspondence course and am having difficulty with the tangent part of the problem. Cheers!
This question is from textbook Algebra and Trigonometry (Sullivan)
Answer by Earlsdon(6294)   (Show Source):
You can put this solution on YOUR website! Find the equation of a circle tangent to the y-axis and whose center is at (-3, 1).
The standard form for a circle of radius r and center at (h, k) is given by:
You are given the center (h, k) as (-3, 1), so h = -3, and k = 1
Now for the radius, r:
Any line that is tangent to (touching) a circle is perpendicular to the radius of the circle.
Since the given circle is tangent to (touching) the y-axis, you know that the radius of the circle is perpendicular to the y-axis and you also know that center is at (-3, 1), so the radius is 3.
Now you can write the equation:
 Simplify this to:
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