Find the 20th term in arithmetic sequence -4, 1, 6, 11, 16,
Mathematics · High School · Tue Nov 03 2020
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- Given the arithmetic sequence:
- -4, 1, 6, 11, 16,
Determine the 20th term.
Formula for arithmetic sequence: an = a1 + (n-1)d
Solution:
Solve first for d or the common difference, this can be done by subtracting the first term to the second term.
d = 1 - (-4)
d = 5
Substitute the values in the given equation. Since we are asked to find the 20th term, n = 20.
a20 = -4 + (20 - 1) 5
a20 = -4 + (19)(5)
a20 = -4 + 95
a20 = 91
The 20th term is 91.