Question
The sum of the 21 terms of the progression:-18,-15,-12
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GPT 3.5
The given arithmetic progression starts with -18 and has a common difference of +3.
To find the sum of the 21 terms, we can use the formula for the sum of an arithmetic series:
S = (n/2)(2a + (n-1)d),
where:
S = sum of the series
n = number of terms
a = first term
d = common difference
In this case, n = 21, a = -18, and d = +3. Plugging these values into the formula, we get:
S = (21/2)(2(-18) + (21-1)(3))
S = (21/2)(-36 + 20(3))
S = (21/2)(-36 + 60)
S = (21/2)(24)
S = 21(12) = 252.
Therefore, the sum of the 21 terms in the given arithmetic progression is 252.
To find the sum of the 21 terms, we can use the formula for the sum of an arithmetic series:
S = (n/2)(2a + (n-1)d),
where:
S = sum of the series
n = number of terms
a = first term
d = common difference
In this case, n = 21, a = -18, and d = +3. Plugging these values into the formula, we get:
S = (21/2)(2(-18) + (21-1)(3))
S = (21/2)(-36 + 20(3))
S = (21/2)(-36 + 60)
S = (21/2)(24)
S = 21(12) = 252.
Therefore, the sum of the 21 terms in the given arithmetic progression is 252.
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