Question

If the nth term of a sequence is 5 + 2n then the sum of first 20 terms is?

Answer 1

Answer:

S(20) = 520

Step-by-step explanation:

given , a(n) = 5+2n

=> a(1) = 5+2(1) = 7

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

=> d = [5+2(n+1) ] - [5 +2n]

=> d= 5 + 2n + 2 - 5 -2n

=> d = 2

S(20) = (20/2) [ 2a + (20-1)d]

S(20) = (10) [ 2×7 + 19×2]

S(20) = (10) [ 14+38] = (10) (52)

S(20) = 520