# $f_x$ is Borel measurable and $f^y$ is continuous then $f$ is Borel measurable

I have to prove the following:

Let $f: \mathbb{R^2}\to \mathbb{R}$ such that $f_x:y\to f(x,y)$ is Borel measurable for all $x\in\mathbb{R}$ and that $f^y:x\to f(x,y)$ is continuous for all $y\in\mathbb{R}$. Prove that $f$ is Borel measurable.

What I have tried to do is to find a sequence of functions $f_n(x,y)$ s.t for a fixed $y$ $f_n(.,y)$ is a linear approximation of $f(.,y)$..

#### Solutions Collecting From Web of "$f_x$ is Borel measurable and $f^y$ is continuous then $f$ is Borel measurable"

By the continuity of $f^y$ we have
$$f(x,y) = \lim_{n \to \infty}f(\lfloor nx \rfloor / n, y).$$
By the measurability of $f^x$, we see that $f$ is the pointwise limit of a sequence of Borel measurable functions, and hence is itself Borel measurable.