There is more than one way to approach (pun absolutely intended) limit problems. We've already looked at graphs and equations.
Another way to estimate the limit of a function is to use a calculator to see what the function approaches as we plug in values of x that get closer and closer to some value a. To keep things organized, now we'll use tables to get the lowdown on functions.
If f(x) = x2, estimate
We make a table. In one column we'll have values of x, and in the next we'll have the corresponding values of f.
First we have x approach 3 from the left.
The values of f(x) in the table appear to be getting closer to 9 as x approaches 3 from the left. We'll see what happens if x approaches 3 from the right.
The values of f(x) appear to be approaching 9 as x approaches 3 from the right, also. We can now shout from the rooftops that, indeed, = 9.
When using tables to determine limits, there's no particular rule about what numbers to plug in for x as it approaches a number a. As long as we look at lots of values of x, and let them get really close (as in, 0.00001 close) to a, we should be fine.