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Engineering

Help me solve this - Sequence and series - JEE Main

If the sum and  product  of the first three terms in an A.P. are 33 and 1155  , respectively , then a value of its 11^{th}  term is :

  • Option 1)

    -35

  • Option 2)

    25

  • Option 3)

    -36

  • Option 4)

    -25

Answers (1)
Views
A Aadil Khan

Let the terms be 

\\a-d,a,a+d\\\\\:then\:\:3a=33\\\\\:a=11\\\\\:(11-d)(11+d)d=1155\\\\\:(121-d^{2})a=1155\\\\\:121-d^{2}=105\\\\\\\:d^{2}=16\\\\\:d=\pm 14

\therefore term =7,11,15\:\:\:or\:\:\:15,11,7\\\\\:t_{11}=a+10d\\\\\:7+10\times4=47

or

\\t_{11}=15+10(-4)\\\\\:15+(-40)\\\\\:=-25

answer = 4


Option 1)

-35

Option 2)

25

Option 3)

-36

Option 4)

-25

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