Step by step
The question
Question: find f(−1/3) for f(x) = 4 − 3x.
f(x) = 4 − 3x
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(−1/3) means: put −1/3 in place of every x.
Every x becomes −1/3.
f(−13) = 4 − 3(−13)
2 Times and divide
Times comes before minus.
Order: ( ) → x² √ → × ÷ → + −
+ × − = −
Plus times minus is minus.
To multiply fractions, we do top times top, and bottom times bottom.
A whole number is a fraction over 1.
= 4 − (−3 × 11 × 3)
3 times 1 is 3.
1 times 3 is 3.
= 4 − (−33)
−3/3 means −3 divided by 3.
That is −1.
= 4 − (−1)
3 Plus and minus
Taking away a negative is the same as adding.
− (−) = +
So 4 − (−1) becomes 4 + 1.
= 4 + 1
4 plus 1 is 5.
f(−13) = 5
So f(−1/3) = 5.
Let's look back.
First: put the number in.
Then: times and divide.
Last: plus and minus.
Answer
f(−13) = 5