Question

the sum of n terms of an AP is 3+n2 then...
1) find first term and sum of first two terms
2) find second, third and 15th term​

Answer 1

For 1st term, n = 1

First term(a) = 3 + (1)² = 4

For 2 first two terms, n = 2

  Sum = 3 + (2)² = 7

⇒ a + (a + d) = 3 + (2)²

⇒ 4 + 4 + d = 3 + 4

⇒ d = - 1

Therefore,

2nd term = a + d = 4 + (-1) = 3

3rd term = a + 2d = 4 + 2(-1) = 2

15th term = a + 14d = 4+14(-1) = - 10

Answer 2

For 1st term, n = 1

For 1st term, n = 1 First term(a) = 3 + (1)² = 4

⇒ a + (a + d) = 3 + (2)²

⇒ a + (a + d) = 3 + (2)

⇒ a + (a + d) = 3 + (2)

2nd term = a + d = 4 + (-1) = 3

3rd term = a + 2d = 4 + 2(-1) = 2

15th term = a + 14d = 4+14(-1) = - 10