When three numbers are in A.P., the middle term is called arithmetic mean (AM) of the two others.
Let a and b are two numbers.
And A be the arithmetic mean between two numbers.
So a A b are in A.P.
or, A – a = b – A
or, 2A = a + b
A =a+b/2
So, in general
A.M. = Sum of the numbers/2 …… (5)
Similarly we can find the two arithmetic means between two number. A1 and A2 are two arithmetic mean between two member a and ‘b’ then a, A1, A2 b are in A.P.
Now using the formula,
tn = a+(n–1)d
or, d = b–a/3 [ here n = 4]
so, A1 = a + d = a +b–a/3 = 2a+b/3
and A2 = a + 2d = a + 2(b–a)/3 = a+2b/3
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