Step by step
The question
Question: find f(4) for f(x) = 3x + 2.
f(x) = 3x + 2
f(x) is read "f of x".
It is a rule, called a function.
A number goes in for x.
The rule gives one answer out.
f(x) = "f of x"
x goes in → an answer comes out
1 Put the number in
f(4) means: put 4 in place of every x.
We write it in brackets.
f(4) = 3(4) + 2
2 Times and divide
Times comes before plus.
Order: ( ) → x² √ → × ÷ → + −
3(4) = 3 × 4
3(4) means 3 times 4.
3 times 4 is 12.
= 12 + 2
3 Plus and minus
12 plus 2 is 14.
f(4) = 14
So f(4) = 14.
Let's look back.
First: put the number in.
Then: times and divide.
Last: plus and minus.
Answer
f(4) = 14