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telo118 [61]
3 years ago
9

What is the first term for an arithmetic sequence with a12 = 56 and a21=101?

Mathematics
1 answer:
Alenkinab [10]3 years ago
4 0
The first term is -43.

Explanation:

an = a + (n - 1)d

a12 = a + 11d = 56, first equation
a21 = a + 20d = 101, second equation

Subtract the second equation from the first equation, cancelling +a and -a
11d - 20d = 56 - 101
-9d = -45
d = 5

Subtitute d into the first equation
a + 99 = 56
a = -43

a refers to the first term, hence the first term is -43.
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