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  • Find the 20thterm of the AP whose 7thterm is 24 less than the 11thterm, first term being 12.

Find the 20th term of the AP whose 7th term is 24 less than the 11thterm, first term being 12.

Answers (1)

Given a = 12 

\\a\textsubscript{7} = a\textsubscript{11} - 24\\ a+6d=a+10d-24 ($using a\textsubscript{n}$ = a + (n-1).d)\\ a - a + 24 = 10d - 6d\\ 24 = 4d \\ d = 6\\

We know that

 a\textsubscript{n} = a + (n - 1)d\\

\\$Put n $= 20, a\textsubscript{20} = a + (20 - 1)d\\ = 12 + (19) \times (6)\\ = 12 + 114\\ =126\\

Hence

 20\textsuperscript{th} \text{ term is } 126

Posted by

infoexpert21

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