Step by step
The question
Question: is y = x³ linear?
y = x³
Linear means: a straight line.
y changes by the same amount every time x goes up by 1.
linear = y changes by the same amount
for each 1 of x
1 Look at the x
There is x cubed.
That bends the line.
= x³ = x × x × x
A table of values shows it.
We put in a few x values and work out y.
2 Check the changes
From one y to the next: plus 1, then plus 7, then plus 19.
The changes are not the same.
So it is not linear.
= not the same → not linear
Careful!
Going up every time is not enough.
A line changes by the same amount every time.
Careful: it goes up every time, but by different amounts
3 Check
Let's check: the changes for each 1 of x are 1, 7, 19.
Not all the same.
So the answer is right!
1, 7, 19: not the same
Let's look back.
First: look at the x.
Then: check the changes.
Last: check.
Answer
Careful: it goes up every time, but by different amounts