Question

Gina started with the circle (x−2)2+y2=16. She translated it 4 units left and 1 unit down. Then she reduced the radius by 1 unit. What is the equation of her new circle?

Answer 1

(x + 2)² + (y + 1)² = 9

Explanation:

Gina started with a circle with the given equation as,

(x - 2)² + (y - 0)² = 16

Since, standard equation of a circle is,

(x - a)² + (y - b)² = r²

Here (a, b) is the center of the circle and 'r' is the radius.

Therefore, from the given equation of the circle,

Center of the circle → (2, 0)

Radius of the circle → √16 = 4 units

She translated this circle 4 units left and 1 unit down.

Rule for the new center after translation will be,

(x, y) → (x - 4, y - 1)

(2, 0) → (2 - 4, 0 - 1)

→ (-2, -1)

Coordinates of the new center → (-2, -1)

Then she reduced the radius by 1 units.

Therefore, radius of the new circle = 4 - 1 = 3 units

Now we substitute these values in the standard equation of the circle to get the equation of the new circle.

(x + 2)² + (y + 1)² = 3²

(x + 2)² + (y + 1)² = 9