22. In an arithmetic series, the common difference is -5 and the sum of 18 terms is 747. Find the first term
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Answer:
189
Step-by-step explanation:
d = -5
S(n) = 747
=> (n/2)(2a + {n - 1}d) = 747
=> (18/2)(2a + {18 - 1}-5) = 747
=> 9(2a + 17*(-5)) = 747
=> 9(2a - 85) = 747 (Minus and plus combine to become minus)
=> 18a - 765 = 747
=> 18a = 747 + 765
=> 18a = 1512
∴ a = 1512/8 => 189
Thus, the first term of an arithmetic series with the common difference -5 and the sum of 18 terms 747 is 189.
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