Question

If n^th term of an a.p. is 7-3n then sum of first 25^ term is

Answer 1

Answer:

800 is the answer.

Last term (n=25) = 7 - 3(25) = -68.

Answer 2

Answer: -800

Step-by-step explanation:

n^th term is aₙ = 7 -3n

∴, first term, a₁ = 7 - (3 × 1) = 4

   25^th term a₂₅ = 7 - (3 × 25) = -68

So, sum of the first 25^th terms is  

     S₂₅ = $\frac{25}{2}$ × (4 + (-68) )

           = $\frac{25}{2}$ × (-64)

           = -800