Question

In an A'P. if the l2th term is -13, ancl the sunr of first four term is24. What is

the sum of the first l0 terms (use fornrula).

Answer 1

Term 13=a+12d=-13=>
a=-12d-13, substitute in sum formula S = n/2[2a+(n-1)d]
24=2[-24d-26+3d]
12=-21d-26
21d=-38=>d=-38/21.substitute for a in first equation.
a=152/7-13=>a=61/7.
Sum of ten no.= 5[132/7+114/7]
=
1230/7