Medium MCQ +4 / -1 PYQ · JEE Mains 2021

Let p and q be two positive numbers such that p + q = 2 and p4+q4 = 272. Then p and q are roots of the equation :

  1. A x<sup>2</sup> – 2x + 8 = 0
  2. B x<sup>2</sup> - 2x + 136=0
  3. C x<sup>2</sup> – 2x + 16 = 0 Correct answer
  4. D x<sup>2</sup> – 2x + 2 = 0

Solution

${p^2} + {q^2} = {(p + q)^2} - 2pq$<br><br>$= 4 - 2pq$<br><br>Now, ${\left( {{p^2} + {q^2}} \right)^2} = {p^4} + {q^4} + 2{p^2}{q^2}$<br><br>$\Rightarrow {\left( {4 - 2pq} \right)^2} = 272 + 2{p^2}{q^2}$<br><br>$\Rightarrow 16 + 4{p^2}{q^2} - 16pq = 272 + 2{p^2}{q^2}$<br><br>$\Rightarrow 2{p^2}{q^2} - 16pq - 256 = 0$<br><br>$\Rightarrow {p^2}{q^2} - 8pq - 128 = 0$<br><br>$\Rightarrow (pq - 16)(pq + 8) = 0$<br><br>$\Rightarrow pq = 16, - 8$ <br/><br/>Here, pq = - 8 is not possible as p and q are positive. <br/><br/>$\therefore$ pq = 16 <br/><br/>Now, the equation whose roots are p and q is <br><br>${x^2} - 2x + 16 = 0$

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

This question is part of PrepWiser's free JEE Main question bank. 223 more solved questions on Complex Numbers and Quadratic Equations are available — start with the harder ones if your accuracy is >70%.

Drill 25 more like these. Every day. Free.

PrepWiser turns these solved questions into a daily practice loop. Chapter-wise drills, full mocks, AI doubt chat. No auto-renew.

Start free →