Which of the following equations represents a circle?

MATHEMATICS · Single correct · CBSE · Mathematics · Conic Sections · Conic Sections

Problem

Which of the following equations represents a circle? (a)

x^2 - y^2 + 4 = 0

(b)

2x^2 + 2y^2 + 4xy - 5 = 0

(c)

3x^2 + 3y^2 + 4x - 5y + 2 = 0

(d)

x^2 + 2y^2 + 3x - 4y + 1 = 0