Step by step
The question
Question: find f(−3) for f(x) = 2x.
f(x) = 2x
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(−3) means: put −3 in place of every x.
We write it in brackets.
The brackets keep the minus with the number.
f(−3) = 2(−3)
2 Multiply
2(−3) = 2 × (−3)
+ × − = −
2(−3) means 2 times −3.
Plus times minus is minus.
2 times 3 is 6.
So we get −6.
f(−3) = −6
So f(−3) = −6.
Let's look back.
First: put the number in.
Last: multiply.
Answer
f(−3) = −6