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Quadratic Equation and Inequalities question

2025 · 3 Apr · Shift 1 · Q34
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  5. /2025 · 3 Apr · Shift 1 · Q34

Quadratic Equation and Inequalities question

2025 · 3 Apr · Shift 1 · Q34

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
Let α\alphaα and β\betaβ be the roots of x2+3x−16=0x^2+\sqrt{3} x-16=0x2+3​x−16=0, and γ\gammaγ and δ\deltaδ be the roots of x2+3x−1=0x^2+3 x-1=0x2+3x−1=0. If Pn=αn+βnP_n=\alpha^n+\beta^nPn​=αn+βn and Qn=γn+o^nQ_n=\gamma^n+\hat{o}^nQn​=γn+o^n, then P25+3P242P23+Q25−Q23Q24\frac{P_{25}+\sqrt{3} P_{24}}{2 P_{23}}+\frac{Q_{25}-Q_{23}}{Q_{24}}2P23​P25​+3​P24​​+Q24​Q25​−Q23​​ is equal to
  1. A
    4
  2. B
    3
  3. C
    5
  4. D
    7
View written solutionFree

Correct answer: C

  1. Given equations and root-sum sequences

We have: x2+3x−16=0x^2+\sqrt{3}x-16=0x2+3​x−16=0 with roots α,β\alpha,\betaα,β, and x2+3x−1=0x^2+3x-1=0x2+3x−1=0 with roots γ,δ\gamma,\deltaγ,δ.

Define Pn=αn+βn,Qn=γn+δn.P_n=\alpha^n+\beta^n, \qquad Q_n=\gamma^n+\delta^n.Pn​=αn+βn,Qn​=γn+δn.

We need to find P25+3P242P23+Q25−Q23Q24.\frac{P_{25}+\sqrt{3}P_{24}}{2P_{23}}+\frac{Q_{25}-Q_{23}}{Q_{24}}.2P23​P25​+3​P24​​+Q24​Q25​−Q23​​.


  1. Recurrence relation for PnP_nPn​

Since α,β\alpha,\betaα,β satisfy x2+3x−16=0,x^2+\sqrt{3}x-16=0,x2+3​x−16=0, we have for each root rrr: r2=−3r+16.r^2=-\sqrt{3}r+16.r2=−3​r+16. Multiplying by rn−2r^{n-2}rn−2, rn=−3rn−1+16rn−2.r^n=-\sqrt{3}r^{n-1}+16r^{n-2}.rn=−3​rn−1+16rn−2. Adding for r=α,βr=\alpha,\betar=α,β gives: Pn=−3Pn−1+16Pn−2.P_n=-\sqrt{3}P_{n-1}+16P_{n-2}.Pn​=−3​Pn−1​+16Pn−2​.

Now compute the required numerator: P25+3P24.P_{25}+\sqrt{3}P_{24}.P25​+3​P24​. Using the recurrence for n=25n=25n=25, P25=−3P24+16P23.P_{25}=-\sqrt{3}P_{24}+16P_{23}.P25​=−3​P24​+16P23​. Hence, P25+3P24=16P23.P_{25}+\sqrt{3}P_{24}=16P_{23}.P25​+3​P24​=16P23​. Therefore, P25+3P242P23=16P232P23=8.\frac{P_{25}+\sqrt{3}P_{24}}{2P_{23}}=\frac{16P_{23}}{2P_{23}}=8.2P23​P25​+3​P24​​=2P23​16P23​​=8.


  1. Recurrence relation for QnQ_nQn​

Since γ,δ\gamma,\deltaγ,δ satisfy x2+3x−1=0,x^2+3x-1=0,x2+3x−1=0, for each root rrr: r2=−3r+1.r^2=-3r+1.r2=−3r+1. Multiplying by rn−2r^{n-2}rn−2, rn=−3rn−1+rn−2.r^n=-3r^{n-1}+r^{n-2}.rn=−3rn−1+rn−2. Adding for r=γ,δr=\gamma,\deltar=γ,δ gives: Qn=−3Qn−1+Qn−2.Q_n=-3Q_{n-1}+Q_{n-2}.Qn​=−3Qn−1​+Qn−2​.

Now for n=25n=25n=25, Q25=−3Q24+Q23.Q_{25}=-3Q_{24}+Q_{23}.Q25​=−3Q24​+Q23​. So, Q25−Q23=−3Q24.Q_{25}-Q_{23}=-3Q_{24}.Q25​−Q23​=−3Q24​. Therefore, Q25−Q23Q24=−3.\frac{Q_{25}-Q_{23}}{Q_{24}}=-3.Q24​Q25​−Q23​​=−3.


  1. Add the two parts

Thus the required value is 8+(−3)=5.8+(-3)=5.8+(−3)=5.


  1. Check with options

The correct option is: 5\boxed{5}5​ which is Option C.


  1. Comparison with stored answer

Stored correct answer: C

Our derived answer: C

So they agree.

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