To express $2x = 5y$ as a function, solve for $y$ in terms of $x$:

$y = \frac{2}{5}x$

Thus, the function is:

$f(x) = \frac{2}{5}x$

Would you like a graph or further explanation?

Here are five related questions:

1. How do you find the inverse of $f(x) = \frac{2}{5}x$?
2. What is the slope and y-intercept of $f(x) = \frac{2}{5}x$?
3. How do you determine if $f(x) = \frac{2}{5}x$ is increasing or decreasing?
4. What are the domain and range of $f(x) = \frac{2}{5}x$?
5. How would the function change if written in terms of $x$ instead of $y$?

Tip:

A function is a relation where each input has exactly one output. Solving for $y$ ensures the equation meets this criterion.