Question

The no of terms in an AP is 40 and the last is -54,given that the sum of the 15 terms added to the sum of the first 30 terms is zero.calculate(1)the first term and common difference.(2)sum of progression

Answer 1

a+39d = -54

S15 = 15/2 (2a+14d)
S30 = 30/2 (2a+29d)
So, 15/2 (2a+14d) + 30/2 (2a+29d) = 0
or, a+12d = 0

Now you have two equations, and you can find a and d, and then the sum S40.

Answer 2

Thanks we'll calculated