Answers

2016-07-20T23:00:27+08:00
An=A1+(n-1)d
80=4+(n-1)4
80=4+4n-4 Cancel the 4 so it will become
80=4n then divide both sides by 4
n=20.

Instead of A1=1 it will become A1=4 because its divisivle by 4 and instead of An=81 it will become An=80 because 81 is not divisible by 4.
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