for what value of c will the circle with equation x^2+6x+y^2-4y+c=0 have a radius of 4?
The center of the circle is found by comparison. It is
The Radius can be found from an equation of a general formula by
Therefore, the reverse can be found by inputting into
Since we know the center, we input and into the above, and get:
Solving for , we get which gives a value for of
Comparison with the general equation of a circle, which is where is the center of the circle, and the radius is per my previous post. When posting formulas, I think it's neater if you arranged them by powers before variables.