Question

Find the number of the terms of the AP - 10 - 7 - 4 -1 so that their sum is 104

Answer 1

here

a= -10

d=3

now put sn=n/2[2a+(n-1)d]

             104=n/2[2*(-10)+(n-1)(-3)]

          208=n[-20+3n-3]

        208=3n^2-23n

           =3n^2-23n-208

   {its ur equation}

now solve the equation and u will get the 2 values of n then put each in sn formula and the answer will be that no. which has rhs=lhs...

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