# Handling minus signs in mathematica

I am doing symbolic manipulations in Mathematica where expressions like

$(-1)^{1/3}\left(-\log z \right)^{2/3}+\log z^{2/3}$

We see that clearly this expression is zero. But Mathematica does not simplifies this expression further. There are many expressions like this that involves a variety of exponent most of which are zero but I want to incorporate this automatically in the code because without evaluating it consumes a huge amount of time.

Thanks!

• "We see that clearly this expression is zero." - not in general, no. That is, unless you're making assumptions on $z$ that you haven't mentioned. Jun 14, 2015 at 20:53
• For example, try $z=i$ and you will find the result is not zero. Jun 14, 2015 at 21:29
• Well, the range of $z\in (0,\infty)$. probably I have to make some assumptions on z, by breaking it up between (0,1) and then from $(1,\infty)$ Jun 14, 2015 at 21:39
• Still not 0; maybe you haven't noticed that $(-1)^{1/3}$ is complex? Here, the principal value of the cube root is not $-1$. Jun 14, 2015 at 22:05
• This seems related: (85893) Jun 15, 2015 at 0:39

(-1)^(1/3) (-Log[x])^(2/3) + Log[x]^(2/3) // FullSimplify[#, x > 1] &


0

Alternatively, using the real-valued cube root of x

CubeRoot[-1] CubeRoot[(-Log[x])^2] + CubeRoot[Log[x]^2]


0

CubeRoot[-1] CubeRoot[-Log[x]]^2 + CubeRoot[Log[x]]^2


0