Question

The nth term of an AP is 1+2n. What is the sum up to the first 20 terms

Answer 1

Step-by-step explanation:

Given,

tn = 1 +2n

=> a+(n-1) d = 1 + 2n

a + (n-1) d = 3 + 2n - 2 = 3 + (n-1) 2

a = 3; d = 2

So,

S(20) = 10/2 [ 2(3) + ( 20 - 1) 2] = 5 ( 6 + 38 )

S(20) = 220