Question

find the sum to n terms of the A.P. , whose kth term is 5k+1....​

Answer 1

Answer:

Solution: As, it is given that k th term of the A.P. is 5k + 1. therefore, ak = a + (k – 1)d ⇒ a + (k – 1)d = 5k + 1 ⇒ a + kd – d = 5k + 1 now, on comparing the coefficient of k, we get, d = 5 and a – d = 1 ⇒ a – 5 = 1 ⇒ a = 6......

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

put the values and find the answer........

sry i cant do full answer because my key board is not working properly......

hope it helps u....

thank u

Answer 2

ak = 5k+1

a1 = 5×1+1 = 5+6 = 6

a2 = 5×2+1 = 10+1 = 11

d = a2-a1 = 11-6 = 5

a = 6 and d = 5

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

= n/2[12+5n-5]

= n/2[7+5n]