What does a dot after a number mean?

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So I'm making some calculations for numerical analysis and the output I get in Wolfram or Mathematica for input like:

-0.666667 (x-1) (x-0.5) (x+0.5)+0.166666 (x-1) (x+1) (x+0.5)+0.499999 (x-1) (x-0.5) (x+1)

Is:

-2.x10^-6 x^3+0.500001 x^2-0.499998 x-2.5x10^-7

So:

$-2.\cdot10^{-6} x^3+0.500001 x^2-0.499998 x-2.5\cdot 10^-7$

My question is, what does this dot in -2.x mean? Does it mean we don't know decimal places or something like that?

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1 Answer

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Wolfram Alpha is trying to tell you that it is not exactly $2$, but very close to $2$. Try using fractions to gain an exact answer:

-2/3 (x-1) (x-1/2) (x+1/2)+ 1/6 (x-1) (x+1) (x+1/2)+ 1/2 (x-1) (x-1/2) (x+1)

Which is $\frac{x^2 - x}{2}$.

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