Progression Practice Test 1

Question : 23 of 23

Marks: +1, -0

Find the sum of the first 14 terms of AP is =7, -3, 1, 5......

Solution:

Let a be the first term and d be the common difference. Number of terms be the n.
So, a = -7, d = ((1 - 3) + (-2)) = 4, n = 14

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

S_14=14/2[2×(-7)+(14-1)4]

= 7( -14 + 52)
⇒ 7 × 38 = 266

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