The sum of the series  1+2\times3+3\times 5+4\times7+.......upto\:\:\:11^{th} term is :

  • Option 1)

    915

  • Option 2)

    946

  • Option 3)

    945

  • Option 4)

    916

 

Answers (1)

\\1+2\times3+3\times5+4\times7 upto\:\:\:11^{th }\:\:term\\\\\\\:

\\\sum_{r=1}^{11}r(2r-1)=\sum_{r=1}^{11}2r^{2}-r\\\\\\\:=2\frac{n(n+1)(2n+1)}{6}-\frac{n(n+1)}{2}\\\\\\\:=2\frac{11\times12\times23}{6}-\frac{11\times126}{2}\\\\\\\:=4\times11\times23-66\\\\\\\:=253\times4-61\\\\\\\:=1012-66\\\\\\\:=946


Option 1)

915

Option 2)

946

Option 3)

945

Option 4)

916

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