Question

sum of first n terms of an arithmetic sequence is n^2+2n. find the first term​

Answer 1

Step-by-step explanation:

n/2 [2a + (n-1)d] = n2+2n

=> 2a + nd - d = 2n+4

by comparing

nd= 2n => d=2

2a-d =4

=> 2a -2 = 4

=> 2a=6=> a=3

so first term is 3