Question

How do you identify the center and the radius of the circle with equation `(x - 3)^2 + (y + 1)^2 = 81`?

Answer 1

centre (3 ,-1) , r=9

Explanation:

The standard form of the equation of a circle is.

`color(red)(|bar(ul(color(white)(a/a)color(black)((x-a)^2+(y-b)^2=r^2)color(white)(a/a)|)))`
where (a ,b) are the coordinates of the centre and r , the radius.

For the given equation: a = 3 , b = -1 and r = 9

hence centre = (3 ,-1) and radius = 9