Let the 2010th term be x
Let the 2011th term be y
Let the 2012th term be z
Since A is the sum of the 2010th term and the 2013th term,
the 2013th term is A-x.
Since B is the sum of the 2010th term and the 2014th term,
the 2014th term is B-x.
So we have these five consecutive Fibonacci terms,
the 2010th, 2011th, 2012th, 2013th, and 2014th:
x, y, z, A-x, B-x
Every Fibonacci term after the 2nd is the sum of the two
preceding terms, so we have these three equations:
(1) z = x + y
(2) (A-x) = y + z
(3) (B-x) = z + (A-x)
From equation (2), which is
A - x = y + z
add x to both sides:
A = x + y + z
Subtract z from both sides
A - z = x + y
and by the equation (1):
z = x + y
So A - z = z since both equal to x + y
add z to both sides:
(4) A = 2z
Simplify (3)
(B-x) = z + (A-x)
B - x = z + A - x
Add x to both sides:
B = z + A
Multiply through by 2
2B = 2z + 2A
From equation (4), substitute A for 2z
2B = A + 2A
2B = 3A
Divide both sides by 2A
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Edwin