Hello help me please
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Answer: the number of terms of the series is 201 numbers
the sum of the first 20 terms is 890
the number of terms of the series is
the series have:
u1 = 5
d = 4
=> u(n) = 5 + 4.(n - 1)
=> u(20) = 5 + 19.4 = 81
so the sum of the first 20 terms is (81 + 5).20/2 = 890
( u1 is the first number of the series, d is the distance between front and rear numbers, u(n) is the overall term of the sequence, u(20) is the 20th of the series)
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