Function of X

`f(x)` means function of `x`.

Which means "Do stuff" to `x`.

NOTE:

What stuff you do and what `x`  is, massively changes what happens.

`f(x)`                     means do stuff to `x`.

`f(x)=x+4`             means the stuff you do to `x`  is add `4`.

`f(2)`                     means do stuff to `x` when `x=2`.

NOTE:

In maths the`f` can be a `g`  or an `h`  or any letter. (Really? Yes really)

Example 1

Given `f(x)=3x+2`  find `f(2)`

This is solved as follows:

`f(x)=3x+2`  means the "Stuff" you do to `x` is multiply it by `3`  and then add `2`.

`f(2)`  means "Do stuff" to `x`  when `x=2`.

So   `f(x)=3x+2`

`f(2)=3(2)+2`

`f(2)=6+2`

`f(2)=8`

Example 2

Given `f(x)=x+4`  find `f(3)`

This is solved as follows:

`f(x)=x+4`  means the "Stuff" you do to `x` is add `4`.

`f(3)`  means "Do stuff" to `x`  when `x=3`.

So   `f(x)=x+4`

`f(3)=3+4`

`f(3)=7`

Example 3

Given `f(x)=3x-1`  find `f(-2)`

This is solved as follows:

`f(x)=3x-1`  means the "Stuff" you do to `x` is multiply it by `3`  and then subtract `1`.

`f(-2)`  means "Do stuff" to `x`  when `x=-2`.

So   `f(x)=3x-1`

`f(-2)=3(-2)-1`

`f(-2)=-6-1`

`f(-2)=-7`

NOTE:

This type of question can be phrased by giving the answer first, see below:

Example 4

If `f(x)=15-4x`  calculate the value of `x`  when `f(x)=35`.

This just says that 

`15-4x=35`

Therefore

`-4x=35-15`

`-4x=20`

`x=20/-4=-5`