$f\colon\sdrta.netbb R^+\to\sdrta.netbb R^+$, $f(x) = x^2$ is injective.$f\colon\sdrta.netbb R\to\sdrta.netbb R$, $f(x) = x^2$ is not injective because $(- x)^2 = x^2$.

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what is the difference in between $\sdrta.netbb R^+$ and also $\sdrta.netbb R$?

Additionally, what is the difference between $\sdrta.netbb N$ and also $\sdrta.netbb N^+$?


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$\sdrta.netbb R^+$ generally denotes the collection of confident real numbers, that is: $$\sdrta.netbb R^+ = \x\in\sdrta.netbb R\mid x>0\$$

It is also denoted by $\sdrta.netbb R^>0,\sdrta.netbb R_+$ and also so on.

For $\sdrta.netbb N$ and $\sdrta.netbb N^+$ the distinction is similar, yet it might be non-existent if you specify $0\notin\sdrta.netbb N$. In many collection theory books $0$ is a natural number, if in analysis it is often not taken into consideration a herbal number. Your mileage might vary top top $\sdrta.netbb N$ vs. $\sdrta.netbb N^+$.


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Simply $\sdrta.netbb R$ means the set of actual numbers.

$\sdrta.netbb R^+$ way the set of positive real numbers.

And $\sdrta.netbb R^-$ method the set of an adverse real numbers.


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