This is a math question, not a Mathematica question. Has to do with adding fractions (general principle: find a common denominator). Probably this should be closed, or maybe migrated if there is an SE group that fields this sort of query.
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Daniel LichtblauJan 9 '13 at 16:56

agree with @DanielLichtblau and of course it is true since 1/(theta -1) + 1 is an alternative form for the left side of the equation.
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StefanJan 9 '13 at 17:06

OP has not defined what $\theta$ and $1$ are and the operations used. It depends on which algebraic structure we are dealing with. division is not defined for Natural Numbers and Integers. While posting these sort of questions, you have to be explicit.
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007resuJan 10 '13 at 2:40

Some one said this is not Mathematica question. TrueQ[x(x-1)==1/(x-1)+1] can be used to check this in mathematica. And it returns FALSE UNLESS YOU SPECIFY X<>1 there.
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007resuJan 10 '13 at 2:43