Step by step
The question
Question: find f(−3) on this graph of f.
f(−3) = ?
1 Look at the graph
The graph shows f.
x goes across.
The height of the graph is f(x): we read it on the y axis.
x: across
f(x): the height, up
2 Read f(−3)
The number in the brackets is the x.
Here x is −3.
f(−3): x = −3 → f(x) = ?
Careful!
f of −3 does not mean a height of −3.
The −3 in the brackets is an x.
So we start at −3 on the x axis.
Careful: f(−3): start at x = −3, not at a height of −3
So f(−3) = −2.
f(−3) = −2
3 Check
Let's check.
The answer gives a point.
(−3, −2) means left 3, then down 2.
It lands on the graph.
So the answer is right!
(−3, −2): left 3, down 2 → on the graph
Let's look back.
First: look at the graph.
Then: read f(−3).
Last: check.
Answer
f(−3) = −2