A function can be written as `f(x)`, which is shorthand for *the function of `x` is such that* followed by an expression for the function eg `f(x) = 2x + 4`. The right hand side states what will be done to `x`: *multiply by 2 and add 4*.

A function is written with a single letter (normally `f`) followed by a variable (normally `x`) in brackets on the left hand side of the equation sign; and an expression (the function to be applied to that variable) on the right hand side.

When a function is *evaluated*, replace the variable with the number: using the above function,

`f(3) = 2 xx 3 + 4 = 10` or

`f(-5) = 2 xx -5 + 4 = -6`

Sometimes the function may be written slightly differently with a colon and an arrow:

`x: → 2x + 4` or even as `x ↦ 2x + 4`.

`f(x)` is defined as `f(x) = 3x^2 + 2`.

What is the value of f(7)?

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

`f(7) = 3(7)^2 + 2`

= 3 x 49 + 2

=149

Answer: 149

Given a function `f(x) = x^2 + 4`, find the value of `f(7)`.

`f(x) = x^2 + 4`

`f(7) = 7^2 + 4` (Replace `x` with 7)

`= 49 + 4`

`= 53`

Answer: 53

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