# Thread: obtaining an equation from the equation of a circle (given a point)

1. ## obtaining an equation from the equation of a circle (given a point)

Answer is to be in the form Ax + By + C = 0

the pines passes through (3,-5) and through the center of the circle

(x+1)^2 + (y-3)^2 = 25/4

2. ## Re: obtaining an equation from the equation of a circle (given a point)

Originally Posted by kingsolomonsgrave
Answer is to be in the form Ax + By + C = 0

the pines passes through (3,-5) and through the center of the circle

(x+1)^2 + (y-3)^2 = 25/4
You should easily be able to find the center of the circle from that equation. If not, look up the standard form of the equation of a circle.

Can you find the line that passes through the two points? Can you at least find the slope?

3. ## Re: obtaining an equation from the equation of a circle (given a point)

the center of the circle is (-1, 3) and the slope is -2 I think so the equation would be y = -2x+1

is that right?

4. ## Re: obtaining an equation from the equation of a circle (given a point)

Originally Posted by kingsolomonsgrave
the center of the circle is (-1, 3) and the slope is -2 I think so the equation would be y = -2x+1
That's correct. But the question said to put the answer in $\displaystyle Ax + By + C = 0$ form, so get everything on one side.

so 2x+y-1=0

6. ## Re: obtaining an equation from the equation of a circle (given a point)

Originally Posted by kingsolomonsgrave
so 2x+y-1=0
Right.

thanks!