Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Sequences and Series question

2025 · 23 Jan · Shift 2 · Q49
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Sequences and Series
  5. /2025 · 23 Jan · Shift 2 · Q49

Sequences and Series question

2025 · 23 Jan · Shift 2 · Q49

JEE MainMathematicsSequences and SeriesNumerical+4 / −1
The roots of the quadratic equation 3x2−px+q=03 x^2-p x+q=03x2−px+q=0 are 10th 10^{\text {th }}10th  and 11th 11^{\text {th }}11th  terms of an arithmetic progression with common difference 32\frac{3}{2}23​. If the sum of the first 11 terms of this arithmetic progression is 88 , then q−2pq-2 pq−2p is equal to ‾\underline{\hspace{2cm}}​ .
Numerical answer
View written solutionFree

Correct answer: 474

  1. Let the arithmetic progression have first term aaa and common difference d=32d=\frac{3}{2}d=23​.

    Then the nnn-th term is Tn=a+(n−1)d.T_n=a+(n-1)d.Tn​=a+(n−1)d.

  2. Write the 10th and 11th terms.

    T10=a+9⋅32=a+272,T_{10}=a+9\cdot \frac{3}{2}=a+\frac{27}{2},T10​=a+9⋅23​=a+227​, T11=a+10⋅32=a+15.T_{11}=a+10\cdot \frac{3}{2}=a+15.T11​=a+10⋅23​=a+15.

    These are the roots of 3x2−px+q=0.3x^2-px+q=0.3x2−px+q=0.

  3. Use the sum of first 11 terms.

    Given S11=112[2a+(11−1)d]=88.S_{11}=\frac{11}{2}\left[2a+(11-1)d\right]=88.S11​=211​[2a+(11−1)d]=88.

    Since d=32d=\frac{3}{2}d=23​, 112(2a+10⋅32)=88.\frac{11}{2}\left(2a+10\cdot \frac{3}{2}\right)=88.211​(2a+10⋅23​)=88.

    112(2a+15)=88.\frac{11}{2}(2a+15)=88.211​(2a+15)=88.

    2a+15=16.2a+15=16.2a+15=16.

    2a=1  ⟹  a=12.2a=1 \implies a=\frac{1}{2}.2a=1⟹a=21​.

  4. Find the two roots explicitly.

    T10=12+272=14,T_{10}=\frac{1}{2}+\frac{27}{2}=14,T10​=21​+227​=14, T11=12+15=312.T_{11}=\frac{1}{2}+15=\frac{31}{2}.T11​=21​+15=231​.

    So the roots are 141414 and 312\frac{31}{2}231​.

  5. Use Vieta's formulas for 3x2−px+q=03x^2-px+q=03x2−px+q=0.

    For a quadratic ax2+bx+c=0ax^2+bx+c=0ax2+bx+c=0:

    • sum of roots =−ba= -\frac{b}{a}=−ab​
    • product of roots =ca= \frac{c}{a}=ac​

    Here, 3x2−px+q=0.3x^2-px+q=0.3x2−px+q=0.

    So, α+β=p3,αβ=q3.\alpha+\beta=\frac{p}{3}, \qquad \alpha\beta=\frac{q}{3}.α+β=3p​,αβ=3q​.

    Now, α+β=14+312=28+312=592,\alpha+\beta=14+\frac{31}{2}=\frac{28+31}{2}=\frac{59}{2},α+β=14+231​=228+31​=259​, hence p3=592  ⟹  p=1772.\frac{p}{3}=\frac{59}{2} \implies p=\frac{177}{2}.3p​=259​⟹p=2177​.

    Also, αβ=14⋅312=7⋅31=217,\alpha\beta=14\cdot \frac{31}{2}=7\cdot 31=217,αβ=14⋅231​=7⋅31=217, hence q3=217  ⟹  q=651.\frac{q}{3}=217 \implies q=651.3q​=217⟹q=651.

  6. Compute q−2pq-2pq−2p.

    q−2p=651−2⋅1772=651−177=474.q-2p=651-2\cdot \frac{177}{2}=651-177=474.q−2p=651−2⋅2177​=651−177=474.

Therefore, 474\boxed{474}474​

PreviousNext

More from Sequences and Series

  • Let Sn​=21​+61​+121​+201​+… upto n terms. If the sum of the first six terms of an A.P. with first term -p and common difference p is 2026 S2025​​, then the absolute difference…2025 · MCQ
  • In an arithmetic progression, if S40​=1030 and S12​=57, then S30​−S10​ is equal to :2025 · MCQ
  • If 7=5+71​(5+α)+721​(5+2α)+731​(5+3α)+…………∞, then the value of α is :2025 · MCQ
  • Let ⟨an​⟩ be a sequence such that a0​=0,a1​=21​ and 2an+2​=5an+1​−3an​,n=0,1,2,3,…. Then k=1∑100​ak​ is equal to2025 · MCQ
  • Let Tr​ be the rth  term of an A.P. If for some m,Tm​=251​, T25​=201​, and 20r=1∑25​ Tr​=13…2025 · MCQ
  • For positive integers n, if 4an​=(n2+5n+6) and Sn​=k=1∑n​(ak​1​), then the value of 507S2025​ is :2025 · MCQ
  • The interior angles of a polygon with n sides, are in an A.P. with common difference 6°. If the largest interior angle of the polygon is 219°, then n is equal to ​.2025 · Numerical
  • Consider an A. P. of positive integers, whose sum of the first three terms is 54 and the sum of the first twenty terms lies between 1600 and 1800. Then its 11th term is :2025 · MCQ