What is the sum of the first 18 terms of the arithmetic sequence 3, 5, 7, 9, 11, …?
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What is the sum of the first 18 terms of the arithmetic sequence 3, 5, 7, 9, 11, …?
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Answer:
360
Step-by-step explanation:
a1 = 3 d = 2 an = 18
an = a1 + (n-1)d
a18 = 3 + (18-1)2
a18 = 3 + (17)2
a18 = 3 + 34
a18 = 37
s18 = n/2 (a1+an)
s18 = 18/2 (3 + 37)
s18 = 9 (40)
s18 = 360
1st term= 3
2nd term= 5
3rd term= 7
4th term= 9
5th term= 11
6th term= 13
7th term= 15
8th term= 17
9th term= 19
10th term= 21
11th term= 23
12th term= 25
13th term= 27
14th term= 29
15th term= 31
16th term= 33
17th term= 35
18th term= 37
Add all of that and the answer will be:
360