Question

if a=3 and T6 = 27 find the sum of the first six terms of the A.P​

Answer 1

Answer:

= 6/2(3+27). =3(30). Therefore, the sum of first six terms of an AP is 90.

Answer 2

Answer:

The sum of 6 terms of the given A.P. is 90

Step-by-step explanation:

Given the first term of the A.P. = 3

and the 6th term is 27

We know that nth term of an A.P. is given by : a + (n - 1) d

where a is the first term

          d is the common difference

          n is the number of terms

on substitution, we get,

27 = 3 + (6 - 1) d

=> 27 - 3 = 5d

=> 24 = 5d

=> d = 24/5

We need to find the sum of 6 terms.

We know that sum of n terms = $\frac{n}{2}$ [2a +(n-1)d]

=> Sum of 6 terms =  $\frac{6}{2}$ [2*3 +(6-1)24/5]

                               = 3 [6 + 5*24/5]

                               = 3[6 + 24]

                               = 3 * 30

                               = 90

Therefore, sum of 6 terms is 90