Question

Which equation represents a circle?

Answer 1

C

Explanation:

The equation of a circle centred at the origin is

x² + y² = r² ← r is the radius

Consider

`(x^2)/(2^2)` +
`(y^2)/(2^2)` = 1, that is

`(x^2)/(4)` +
`(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