# Circle Equation

• Mar 26th 2011, 03:09 PM
thamathkid1729
Circle Equation
Find an equation for the circle that goes through the points (0
, 0), (0, 8), and (6, 12). Find an equation for the line that is tangent to this circle at (6, 12).

• Mar 26th 2011, 03:13 PM
Plato
Quote:

Originally Posted by thamathkid1729
Find an equation for the circle that goes through the points (0
, 0), (0, 8), and (6, 12). Find an equation for the line that is tangent to this circle at (6, 12).

You have enough other postings to understand that this is not a homework service nor is it a tutorial service. Please either post some of your own work on these problems or explain what you do not understand about the question.
• Mar 27th 2011, 12:02 AM
mathfun
A circle has equation ${x^2} + {y^2} + Ax + By + C = 0$ $A,B,C \in {\Cal R}$.
You have three points given and three unknown letters( A,B,C). Find them.
Then the equation of the tangent is $\left( {x - {x_0}} \right)\left( {{x_1} - {x_0}} \right) + \left( {y - {y_0}} \right)\left( {{y_1} - {y_0}} \right) =
{r^2}$

where x0,y0 is the center of the circle
x1,y1 the tangency point and r its radius