Please ans question no 9

9 .       T h e   s u m   o f   7 2 × 3   1 3   +   9 3 × 4   1 3 2   +   11 4 × 5   1 3 3   +   . . .   u p t o   10   t e r m s   i s   e q u a l   t o   ( A )     1 2   -   1 12 × 3 10                                                                                         ( B )     1 3   -   1 12 × 3 10 ( C )     1 2   -   1 10 × 3 10                                                                                           ( D )       n o n e   o f   t h e s e    


 

Dear Student,
Please find below the solution to the asked query:

We haveS=72×313+93×4132+114×5133+.....+10 termsNow7,9,11 or 2,3,4 or 3,4,5 are all Arithmetic ProgressionHence general term of series Tr=2r+5r+1r+213r=2r+5r+1r+213r=3r+6-r+1r+1r+213r=3r+6r+1r+2-r+1r+1r+213r=3r+1-1r+213r=3r+113r-1r+213r=1r+113r-1-1r+213rS10=r=110 1r+113r-1-1r+213r= 12-1313+1313-14132+14132-15133+....+111139-1121310=12-1313+1313-14132+14132-15133+....+111139-1121310=12-1121310 Answer

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