Q46 / 125 · BITSAT 2017 · Mathematics

For the equation 3x2+px+3=0,p>0, if one of the roots is square of the other, then p is equal to

  • A
    12
  • B
    1
  • Correct answer
    C
    3
  • D
    23

Solution

Let α,α2 be the roots of 3x2+px+3

∴ Product of the roots, 

α·α2=1⇒α3=1

Again, α+α2=-p3

⇒ 1+1=-p3   (if α=1)

⇒ p=-6

But p>0

∴ α=1 is not possible.

If α=ω, then α+α2=ω+ω2=-1

∴ -1=-p3⇒p=3

Again, if α=ω2, then

α+α2=ω2+ω4=ω2+ω=-1

∴ -1=-p3

⇒ p=3

Hence, the correct answer is option: 'C'.

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