Question

If equation (a + 1)x² + (b – 1)y² + (a – 2b)xy – 6x + 9y – 3 = 0 represent a circle then its radius is

• A. 3/2
• B. 2/3
• C. 1
• D. $\sqrt { a ^ { 2 } + b ^ { 2 } }$

Answer 1

Answer: (A)

3/2

Answer 2

a + 1 = b – 1 & a = 2b Ž a = – 4, b = –2

Ž Circle –3x² – 3y² – 6x + 9y – 3 = 0

or

x² + y² + 2x – 3y + 1 = 0