Math, asked by dattubhai, 1 year ago

In the A.P. 7,14,21,... How many terms are to be consideredfor getting sum 5740. (ans:40)

Answers

Answered by Anonymous

5740=n/2(14+(n-1)7)
solving this will give u 2 and but negative should be excluded

dattubhai: then

Anonymous: put b= -1

Anonymous: a=1

dattubhai: who says

Anonymous: c=1680

dattubhai: ok

dattubhai: a=n^2 and b=n

Lazarus: Atharva Shetty the value of c=1640 and not 1680 Bro! !

Anonymous: by mistake i wrote that

dattubhai: i know that

Answered by Lazarus

ACCORDING TO THE FORMULA
Sn= n/2 (2a+(n-1)*d)
5740 = n/2 (2*7+(n-1)*7)
5740 =n/2 (14+7n-7)
5740*2=n (7+7n)
Or,7n^2+7n=11480
Or, n^2+n-1640
Using Sridhara Acharya formula(done in my notebook sorry can't show the process to you.) Therefore n= 4 but n is not equal to -10/2
because n being the no. of terms cannot be negative, not possible.
So,4 terms are required for getting the sum of AP 5740.

dattubhai: sorry the ans is 40

Lazarus: How!!

dattubhai: you do the sum and find s40 ok and see

Lazarus: Yeah my mistake!!!

Lazarus: I usually never do this sorry Bro! !

Lazarus: Ask for more questions if you stuck . perhaps I can help you wit

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