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Question: If4a<sup>2</sup> + 9b<sup>2</sup> – c<sup>2</sup> + 12ab = 0, then the family of straight lines ax ...

If4a2 + 9b2 – c2 + 12ab = 0, then the family of straight lines

ax + by + c = 0 is concurrent at :

A

(2, 3) or (–2, – 3)

B

(2, 3) or (2, – 3)

C

(–2, 3) or (–2, –3)

D

(– 2, 3) or (2, – 3)

Answer

(2, 3) or (–2, – 3)

Explanation

Solution

ince 4a2 + 9b2 – c2 + 12ab = 0

Ž (2a + 3b)2 – c2 = 0

Ž (2a + 3b + c) (2a + 3b – c) = 0

Ž 2a + 3b + c = 0

or 2a + 3b – c = 0

Ž – 2a – 3b + c = 0

\ ax + by + c is concurrent at

(2, 3) or (– 2, – 3)