Continuity and limits at end point of interval I am bad a calculus and I have question about continuity. If I have a polynomial, then the function is continuous on $\mathbb{R}$ because $\lim_{x\to a} f(x) = f(a)$ for all $a\in \mathbb{R}$.
My question is if $f(x) = \sqrt{x}$ is continuous at $0$. My text book doesn't say if this is continuous at $0$. It does say that the function is continuous from the right. But I have also heard that continuity is a more general concept.
My question is: under the real definition of continuity, if $f(x) = \sqrt{x}$ continuous at $0$?
Is it correct to say that $\lim_{x\to 0} \sqrt{x} = 0$ without specifying that $x$ is approaching from the right?

It all depends on where the function is defined. In your example, the function is not defined for negative numbers. And at zero, the value of function is zero.
 And since you can approach zero, from the direction where function is defined, that is from right, the value goes tends to zero. Hence the function is continuous. Meaning continuous on all points where it is defined. But at zero, left continuity doesn't exist at zero. So according to the real definition of continuity, it is not continuous at zero
