Understanding Functions If there exists a definite rule f which associates each element of x to a unique element y, then this rule f is called a real valued function and is denoted by f(x) Share this:Click to share on Facebook (Opens in new window)Click to share on Twitter (Opens in new window)Click to share on Google+ (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Reddit (Opens in new window)