Question

What is the radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0?

Answer 1

Answer:

2 units

Step-by-step explanation:

The given equation of the circle is:

$x^{2} + y^{2}+8x-6y+21=0$

The general equation of the circle is:

$x^{2} + y^{2}+2gx+2fy+c=0$

Comparing the given equation with the general equation we can say:

g = 4

f = -3

c = 21

The formula for radius of the circle is:

$radius=\sqrt{g^{2} +f^{2} -c }$

Using these values of the given circle, we get:

$radius=\sqrt{(4)^{2}+(-3)^{2}-21}\\\\radius=\sqrt{4}\\\\radius=2$

Therefore, the length of radius of the given circle is 2.