Step by step
The question
Question: is {(0, 0), (1, 1), (1, −1), (4, 2)} a function?
{(0, 0), (1, 1), (1, −1), (4, 2)}
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.
0 goes to 0.
0 → 0
1 goes to 1 and −1.
One x, two different y's!
1 → 1, −1
4 goes to 2.
4 → 2
2 Read the answer
1 has two y's.
So it is not a function.
= no, not a function
3 Check
Let's check on a grid.
Draw the grid.
We plot the points.
A straight up-and-down line at x = 1 meets two points.
Two points on one up-and-down line: not a function.
The same answer!
Let's look back.
First: each x and its y.
Then: read the answer.
Last: check.
Answer
= no, not a function