Question

The equation x2 + y² - 6x + 2y = b describes a circle.

If the radius of the circle is 4 units, what is the value of b in the equation above?

Answer 1

Explanation:

given equation of a circle : x^2+y^2-6x+2y=b.

BY comparing it with x^2+y^2+2gx+2fy+c=0, we get

centre as (-g,-f)=(3,-1)

Since we know that radius r=sqrt(g^2+f^2-c)

Here radius is given as 4 units.

So,

4=sqrt((3)^2+(-1)^2-c)

=>16=9+1-c

Therefore, c=-6