Question

If the centre of the circle is (-a, -b) and radius is √(a² - b²) then the equation of circle is: 

(a) x² + y² + 2ax + 2by + 2b² = 0 

(b) x² + y² + 2ax + 2by – 2b² = 0 

(c) x² + y² – 2ax – 2by – 2b² = 0 

(d) x² + y² – 2ax – 2by + 2b² = 0

Answer 1

(a) x² + y² + 2ax + 2by + 2b² = 0 

Equation of the circle is (x – h)² + (y – k)² = r² 

⇒ (x + a)² + (y + b)² = a² – b² 

⇒ x² + y² + 2ax + 2by + a² + b² = a² – b² 

⇒ x² + y² + 2ax + 2by + 2b² = 0