# Very quick question

1. Jan 3, 2008

### thomas49th

When you say f(x) = x² + 4 (the function of f is defined at x² + 4)
is that the same as saying y = x² + 4???

2. Jan 3, 2008

### slider142

Only if you set y=f(x). f(x) is a function assigning the value f(x) to each input x. y = f(x) is just an equation, which can be graphed on a Cartesian plane; it is a method of visualizing the properties of the function.

3. Jan 4, 2008

### HallsofIvy

Staff Emeritus
Did you mean "defined as $x^2+ 4$.

No, that is NOT the same as saying "y= $x^2+ 4$" unless, as slider142 said, you define y= f(x). If you are graphing such a function on an standard "xy coordinates sytem" then the first thing you should say is "let y= f(x)". That is so standard that it is not always said.