Question

Find the sum of 1st 18 terms of an AP whose nth term is 3-2n.

Answer 1

-288

Explanation:

Given AP

• t(n) = 3 - 2n

To find,

• The sum of first 18 terms

Solution

• Sn = 1/2n(t(1) + t(n))

The first and 18th terms as per the formula

• t(1) = 3 - 2 = 1
• t(18) = 3 - 18*2 = 3 - 36 = -33
• S18 = 1/2*18(1 - 33) = 9*(-32) = -288

Answer is -288