1.

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»

(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



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