Question

Find the first term and the common difference of an AP iif the sum of the first n term is n (5n +7) 12

Answer 1

Sum of 1 term = a = 5×1 +7 = 12

sum of 2 terms = 5×2 +7 = 17

2nd term = 17-12 = 5

d = t2-a = 5-12 = (-7)