Step by step
The question
Question: find the limit as x → 5 of (x² − 25)/(x − 5), using a table.
1 Try x = 5
First, try x = 5 itself.
The top is 0, and the bottom is 0.
We cannot divide by 0.
So f(x) has no value at 5.
But a limit does not need the value at 5.
It asks: as x gets close to 5, what number does f(x) get close to?
Careful!
0/0 does not mean there is no limit.
It only means we must look closer.
2 From the left
Take numbers just below 5: 4.9, 4.99, 4.999.
They come closer and closer to 5.
Put 4.9 in: we get 9.9.
The others the same way, with a calculator.
From the left, f(x) gets close to 10.
3 From the right
Now numbers just above 5: 5.1, 5.01, 5.001.
Work out f(x) for each one.
From the right, f(x) gets close to 10 too.
4 Read the limit
Both sides get close to the same number.
So the limit is 10.
5 Check
Let's check with numbers even closer.
x = 4.9999 gives 9.9999.
x = 5.0001 gives 10.0001.
Still close to 10.
Right!
Let's look back.
First: try x = 5.
Then: from the left.
Then: from the right.
Then: read the limit.
Last: check.