Question

In snow AP, the sum of its first n terms is n^2+2n. Find it's 18^th term

Answer 1

Answer: the 18 the term is 37

Step-by-step explanation:

Sn = n^2 +2n

S1 = 1^2 + 2 x 1

S1 = 1+2=3 ———-> a1

S2 = 2^2+ 2 x 2

S2= 4+4=8

S2- S1 = a2

a2 = 8-3=5

common difference = a2-a1

= 5-3

= 2

a18 = a+ ( n-1) d

= 3 +(18-1)2

= 3+(17)2

= 3+34

= 37

Therefore a18 is 37

I hope it helps u