I've got the term $-1 + 2b^2 + 2b\sqrt {b^2-1}$ appearing several times within several larger expressions. It is easy to see that this expression factors into ${(b+\sqrt{b^2-1})^2}$, but when I use FullSimplify or Factor it doesn't change. Is there a way to make Mathematica factor this expression automatically? $b$ is defined to be real and $>1$.


1 Answer 1


The following, although rather unsatisfying, does produce the desired result.

term = -1 + 2 b^2 + 2 b Sqrt[b^2 - 1]
Factor[Simplify[term /. b -> Cosh[z], Sinh[z] > 0] // TrigExpand]
    /. Sinh[z] -> Sqrt[Cosh[z]^2 - 1] /. Cosh[z] -> b
(* (b + Sqrt[-1 + b^2])^2 *)

Indeed, the second expression, with a LeafCount of 13, is simpler than the first, with a LeafCount of 19.

Depending on the details of the actual problem you wish to solve, working with hyperbolic functions throughout instead of b might be preferable.


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