Question

 In an AP Given a₁₂ = 37, d = 3, find a and S₁₂.

Answer 1

Given that, a₁₂ = 37, d = 3

As a_n = a + (n − 1)d,

a₁₂ = a + (12 − 1)3 

37 = a + 11d

37 = a + 11 × 3

37 = a + 33

a = 37 - 33

a = 4

`S_n = n/2 [a+a_n]`

`S_n = 12/2 [4+37]` 

`S_n = 6(41)`

`S_n = 246`

Thus, a = 4 and S₁₂ = 246