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BITSAT 2017
Exam
BITSAT
Year
2017
Subject
Mathematics
Chapter
Quadratic Equation

BITSAT 2017 · Mathematics · Quadratic Equation

For the equation 3x^ 2 + px + 3 = 0, p > 0 , if one of the roots is...

For the equation 3x2+px+3=0,p>03x^{2} + px + 3 = 0, p > 0, if one of the roots is square of the other, then pp is equal to

Options

  1. A12\dfrac{1}{2}
  2. B11
  3. C33
  4. D23\dfrac{2}{3}

Correct answer

C. 33

Step-by-step solution

Let α,α2\alpha, {\alpha}^{2} be the roots of 3x2+px+33x^{2} + px + 3

∴∴ Product of the roots,&

α⋅α2=1⇒α3=1\alpha \cdot {\alpha}^{2} = 1 ⇒ {\alpha}^{3} = 1

Again, α+α2=−p3\alpha + {\alpha}^{2} = - \dfrac{p}{3}

⇒1+1=−p3⇒ 1 + 1 = - \dfrac{p}{3} & (if α=1\alpha = 1)

⇒p=−6⇒ p = - 6

But p>0p > 0

∴α=1∴ \alpha = 1 is not possible.

If α=ω\alpha = \omega, then α+α2=ω+ω2=−1\alpha + {\alpha}^{2} = \omega + {ω}^{2} = - 1

∴−1=−p3⇒p=3∴ - 1 = - \dfrac{p}{3} ⇒ p = 3

Again, if α=ω2\alpha = {ω}^{2}, then

α+α2=ω2+ω4=ω2+ω=−1\alpha + {\alpha}^{2} = {ω}^{2} + {ω}^{4} = {ω}^{2} + \omega = - 1

∴−1=−p3∴ - 1 = - \dfrac{p}{3}

⇒p=3⇒ p = 3

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