Question

find the sum of n terms of an ap whose rth term is (5r+1)​

Answer 1

Answer:

(7+5n)n/2

Step-by-step explanation:

a =  5 +1 =6

a2 = 10+1 =11 d= a2-a = 11-6 =5

sn = [2a+(n-1)d]n/2

=[12+(n-1)5 ]n/2

=(12 +5n-5 )n/2

(7+5n)n/2

Answer 2

Answer:

Step-by-step explanation:

a  =6

d= 5

=[12+(n-1)5 ]n/2

=(12 +5n-5 )n/2

(7+5n)n/2