Question

the first term of an ap is 4 and nth term is 40 find the sum of first 20 terms​

Answer 1

Answer:

The sum of first 20 terms is 440

Step-by-step explanation:

Given that first term = a = 4

nth term = aₙ = 40

We know that for an AP,

aₙ = a + (n - 1)d

=> 40 = 4 + (n - 1)d

=> 36 = (n - 1)d                              

We need to find the sum of first 20 terms = S₂₀

We know that Sₙ = $\frac{n}{2}$ [2a + (n - 1)d]

=> Sₙ = $\frac{20}{2}$ [2* 4 + 36]                      (as (n - 1)d = 36)

         = 10 * [8 + 36]

         = 10 * 44

         = 440

Therefore, the sum of first 20 terms is 440