If there are n terms, we have
a + ar = x
ar^(n-2) + ar^(n-1) = y
a(1+r) = x
ar^(n-2)(1+r) = y
now divide
r^(n-2) = y/x
r = (y/x)^(n-2)
the sum of the first two term of a gp is x and the sum of the last two term of the gp is y,find the common ratio
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