Question

n=11,l=221and middle term=121 find Sn
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Answer 1

Answer:

Total terms of. given A.P ( n) = 11

Last term of AP (l). = 221

Middle term of AP = 121

Middle term = 6th term

last term. = 11 th term

So , 6th term = 121 = a + 5d ( eq 1)

11th term = 221 = a + 10 d. (eq. 2)

Now Substracting eq 1 from eq 2 nd

a + 10 d. = 221

+ a. + 5 d. = 121

-. -. -

________________

5d. = 100

Putting the value of a in eq 1 st

a + 5( 100) = 121

a +500. = 121

a. = 121 - 500

a = -379

Sn = n/2( a+l )

Sn.= 11/2 (-376 + 221 )

Sn. = 11/2( -158)

Sn = 11 × - 79

Sn = - 869

So , Sum of 11 terms of given AP is - 869

Hope it may help you ♥

@shorya 9017☆☆☆☆

Answer 2

....I think it helps u...

answer is -869 ans.....

vishakaa