Question

Which of the following is an equation of the circle in

the xy-plane that has center (0,0) and radius 4?
A) x2 + y2 = 4
B) x2 + y2 = 8
C) x2 + y2 = 16
D) x2 + y2 = 64​

Answer 1

C). x^2 + y^2 = 16.

Explanation:

The equation of a circle with center (0, 0) and radius r is

x^2 + y^2 = r^2

So our equation (with r = 4) is:

x^2 + y^2 = 4^2

x^2 + y^2 = 16.

Answer 2

C

Explanation:

The equation of a circle centred at the origin is

x² + y² = r² ← where r is the radius

here r = 4, thus

x² + y² = 4², that is

x² + y² = 16 → C