Question

Sum of first n terms of an arithmetic sequence is
3n2_ 6n.
a) Calculate first term and common difference?
b) Write the algebraic form?
c) Find its 15th term?

Answer 1

Answer:

= 3 + 6n

Step-by-step explanation:

Sn = 3n^2 + 6n

=> n/2 [ 2a + (n-1) d] = n (3n + 6)

=> [ 2a + (n-1) d] = 2 (3n +6)

=> 2a + (n-1) d = 6n + 12

=> 2a + (n-1)d = 18 + 6n - 6

=> 2a + (n-1)d = 18 + 6(n-1)

On Comparing both sides, we get

2a = 18

=> a = 9

And, d = 6

Tn = a + (n-1) d

= 9 + (n-1) 6

= 9 + 6n - 6

= 3 + 6n