Since , for
we have
The limit of the left and right expressions as
goes to infinity is
, so the same holds for the middle, by the squeeze theorem.
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Try putting $x=0^+$ (meaning a bit larger than zero) and $x=0^-$ (a bit smaller than zero) and see what happens.
in the first case, $-1<x-1<0$ and so $[x-1]=-1$ and with a similair argument, $[1-x]=0$
And so in the first example, if $x$ is a bit larger than $0$, the result is $0$.
Do the same thing when $x=0^-$ to see if it is the same answer. if it is, then the answer is $0$. if it isn't, then there is no limit.
If $L$ us the value of your limit, then using the fact that $[x+n]=[x]+n$ for all $x\in\mathbb R, n\in\mathbb Z$, you'll have $$L=\lim_{x\to 0}(1-x+[x]-1+1+[-x])=\lim_{x\to 0}(1-x+[x]+[-x])=\lim_{x\to 0}(1-x-1)=0.$$
Since we are interested in the behavior of $\left\lfloor 3x-\frac{1}{2}\right\rfloor$ as $x$ tends to $\frac{1}{2}$ from the left, we may assume that $\frac{1}{6}<x<\frac{1}{2}$. Then
$$\frac{3}{6}<3x<\frac{3}{2}$$
so
$$\frac{3}{6}-\frac{1}{2}<3x-\frac{1}{2}<\frac{3}{2}-\frac{1}{2}$$
which reduces to $0<3x-\frac{1}{2}<1$. It follows that $\left\lfloor 3x-\frac{1}{2}\right\rfloor=0$, so
$$\lim_{x\to\frac{1}{2}^-}\left\lfloor 3x-\frac{1}{2}\right\rfloor=0$$
Hint: The function $g(x)=3x-\frac12$ is increasing, and hence, for $\frac16\le x<\frac12$, we have $g\left(\frac16\right)\le g(x)<g\left(\frac12\right)$.