Step by step
The question
Question: is {(1, 5), (2, 5), (3, 5), (4, 5)} a function?
{(1, 5), (2, 5), (3, 5), (4, 5)}
A function is a rule where each x has only one y.
One x in, one y out.
function: each x has only one y
1 Each x and its y
We take each x and see where it goes.
1 goes to 5.
1 → 5
2 goes to 5.
2 → 5
3 goes to 5.
3 → 5
4 goes to 5.
4 → 5
Careful!
5 comes out twice, from two different x's.
That is fine.
Only one x with two y's breaks the rule.
Careful: the same y twice is fine (5)
2 Read the answer
Every x has only one y.
So yes, it is a function.
= yes, a function
3 Check
Let's check on a grid.
Draw the grid.
We plot the points.
A straight up-and-down line meets at most one point.
Here at x = 1: one point.
No up-and-down line meets two points.
It is a function.
The same answer!
Let's look back.
First: each x and its y.
Then: read the answer.
Last: check.
Answer
= yes, a function