Question

find the sum of nth term of ap whose kth term is 5k+1

Answer 1

Hope it helps...!!!

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It is given that the kth term of the A.P. is 5k + 1.
kth term = ak = a + (k – 1)d
∴ a + (k – 1)d = 5k + 1
a + kd – d = 5k + 1

Comparing the coefficient of k, we obtain d = 5
a – d = 1
⇒ a – 5 = 1
⇒ a = 6
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Therefore,
Answer: n/2 (5n+7)
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#Be Brainly✌️

Answer 2

Ak = 5k+1

Ak-1= 5(k-1)+1

d = Ak - Ak-1

= 5k +1 -( 5(k-1)+1)

= 5k +1 - 5k +5 -1

= 5

A1= 5(1)+1 = 6

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

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

= n/2 (5n +7)