Question

Which equation represents a circle?

Answer 1

Answer:

C

Step-by-step explanation:

The equation of a circle centred at the origin is

x² + y² = r² ← r is the radius

Consider

$\frac{x^2}{2^2}$ + $\frac{y^2}{2^2}$ = 1, that is

$\frac{x^2}{4}$ + $\frac{y^2}{4}$ = 1

Multiply through by 4

x² + y² = 4 ← equation of circle

This is the equation of a circle centred at the origin with radius 2