Answers

2016-06-29T07:06:12+08:00
An = a₁ + (n-1)d
b = a + (3-1)d
b = a +3d -d
b-a = 2d
b-a/2 = d (common difference)

an = a₁ + (n-1)d
a₂ = a + (2-1)b-a/2
a₂ = a + b-a/2
a₂ = a+b/2 (arithmetic mean)


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