Q7 of 82 Page 4

Find the value of p so that the quadratic equation px (x- 3) + 9 = 0 has two equal roots. (CBSE 2011)

Given, px (x – 3) + 9 = 0

⇒ px2 – 3px + 9 = 0


For equal roots, the value of discriminant should be zero i.e.,


D = b2 – 4ac = 0


Here, a = p, b = -3p, c = 9


⇒ D = (-3p)2 – 4(p)(9) = 0


⇒ 9p2 – 36p = 0


⇒ 9p (p – 4) = 0


⸫ p = 0 or 4


⸫ p = 4 [⸪ coefficient of x2 cannot be zero]

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