Question

find the sum of ap of 12 terms who's first and last terms are 3 and 36​

Answer 1

a = 3 (first term)

Tn = 36 (last term)

n = number of terms is given 12

d = common difference = ?????

Formula :-

Tn = a + (n-1)d

36 = 3 + (12-1)d

36 = 3 + 11d

36 - 3 = 11d

33 = 11d

d = 33/11

d = 3

Now, formula to find sum

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

Sn = 12/2 [2(3) + (12-1)3]

Sn = 6[6 + 33]

Sn = 6*39

Sn = 234