Find the sum of the following APs.
− 37, − 33, − 29 ,…, to 12 terms
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Solution
−37, −33, −29 ,…, to 12 terms
For this A.P.,
a = −37
d = a2 − a1 = (−33) − (−37)
= − 33 + 37 = 4
n = 12
We know that,
Sn = `n/2 [2a + (n - 1) d]`
S12 = `12/2 [2(-37) + (12 - 1) × 4]`
= 6[-74 + 11 × 4]
= 6[-74 + 44]
= 6(-30) = -180
Concept: Sum of First n Terms of an AP
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