how am i supposed to sum the series 1.3.5+3.5.7+5.7.9 ......n terms without usin Sn -Sn=0 as a method. Like another method is given in hall n knight chp. i need an explaination for that method. Please help me with that method if possible or else ne other method will do!

take the second number of the first term.

now we can say that for n=1, it is 2n+1

the whole expression becomes (2n-1)(2n+1)(2n+3)

use sumation and the formulas u already mus be knowing.

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Rahul- IIT Roorkee

Simply verify the options by considering n=2 or more than thatDifficult to understand - post it here and we will get you the answer and detailed solution very quickly. We are all IITians and here to help you in your IIT JEE preparation.DO APPROVE IF THE ANSWER HELPS YOU.Now you can win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian.Regards,