Question

Find the sum of the first 15 terms of an ap whose nth term is 3-2n

Answer 1

Given:  nth term is 3-2n

To find: the sum of the first 15 terms of an ap

Solution:

• Now we have given the nth term of AP as: 3 - 2n

• Lets put n = 1, we get :

               a1 = 3 - 2 = 1

• Lets put n = 2, we get

               a2 = 3 - 4 = - 1

• Now from these two terms, we get common difference as:

               d = -1 - 1

               d = -2

• Lets put n = 15, we get

               a15 = 3 - 30

               a15 = -27

• So the sum of 15 terms will be: n/2(a+l)

               Sum = (15/2)[1 + (-27)]

               Sum = (15/2) × - 26

               Sum = -195

Answer:

               So the sum of 15 terms is -195

Answer 2

Step-by-step explanation:

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