How many terms of the AP 26,21,16,11,.... are needed to give the sum 1

1.	How many terms of the AP 26,21,16,11,.... are needed to give the sum 11?
Answer» \'a\' or the first term=26and \'d\' or the common difference =21-26=-5n=?Sum of n terms of A.P=11Sum of n terms of A.P=n/2(2a+(n-1)d11=n/2(52-5n+5)22=n(57-5n)22=57n-5n25n2-57n+22=0By splitting the middle term,5n2-55n-2n+22=05n(n-11)-2(n-11)=0(5n-2)(n-11)=0n-11=0n=11

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