Functions · Second Year
Functions
Second Year · Evaluating and solving f(x) · Tap NEXT to begin
Section 1 of 2
Evaluating a Function
A function is a rule. $f(x)$ means ‘put the number in place of $x$’.
Worked example — find f of a number
For $f(x) = 3x + 5$, find $f(7)$.
$f(7) = 3(7) + 5 = 21 + 5$
$f(7) = 26$
Now you try
You try
For $f(x) = 2x - 7$, find $f(1)$ and $f(5)$.
Pen and paper out — try it before you reveal.
$f(1) = 2(1) - 7 = -5$
$f(5) = 2(5) - 7 = 3$
$f(1) = -5$, $f(5) = 3$
$f(1) = -5$, $f(5) = 3$
Section 2 of 2
Working Backwards
If you know the output, put the rule equal to it and solve for $x$.
You try
For $f(x) = 3x + 5$, find $x$ when $f(x) = 39$.
Pen and paper out — try it before you reveal.
$3x + 5 = 39$
$3x = 34$
$x = \dfrac{34}{3}$
$x = \dfrac{34}{3}$
That’s Functions.
Substitute a number to evaluate $f(x)$, or set the rule equal to a value and solve backwards.