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What is the sum of the first 25 terms of an AP whose nth term is given by t = 2 - 3n?

Published in Arithmetic Progressions 1 min read

The sum of the first 25 terms of the Arithmetic Progression (AP) is -925.

We are given that the nth term of the AP is defined as t = 2 - 3n. This means an = 2 - 3n. To find the sum of the first 25 terms, we can use the formula for the sum of an AP.

Here's how to determine the sum:

  1. Find the first term (a1):
    Substitute n = 1 into the formula for the nth term:
    a1 = 2 - 3(1) = 2 - 3 = -1

  2. Find the 25th term (a25):
    Substitute n = 25 into the formula for the nth term:
    a25 = 2 - 3(25) = 2 - 75 = -73

  3. Use the formula for the sum of the first n terms of an AP:
    Sn = n/2 * (a1 + an)

    In this case, n = 25, a1 = -1, and a25 = -73. Therefore:
    S25 = 25/2 (-1 + (-73))
    S25 = 25/2
    (-74)
    S25 = 25 * (-37)
    S25 = -925

Therefore, the sum of the first 25 terms of the AP is -925, as confirmed by the reference provided: "Therefore, sum of first 25 term is −925."

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