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### Course: Differential Calculus>Unit 1

Lesson 3: Estimating limits from tables

# Estimating limits from tables

When given a table of values for a function, we can estimate the limit at a certain point by observing the values the function approaches from both sides. The limit is the value the function converges to, even if the function's value at that point is different.

## Want to join the conversation?

• My gut says that there must be a function f(x) that gives us this exact table but has the value of 6.37 as its limit. We can't know for sure if the function suddenly (but continuously!) shoots up to 6.37 and back down again or not. So why exactly is it a reasonable estimate to say it doesn't?
• From the author:I agree with you. We definitely don't know for sure just with a table (which only samples the function). But in this example, we need to pick the most reasonable estimate, and, in general, it is usually most reasonable to assume that something wacky doesn't happen unless it is explicitly pointed out.
• Can someone explain why 3.68 is a better estimate than 4 for the limit?
• Because 3.68 is more accurate than 4.
3.68 probably isn't the exact limit either, but given the table it is our best bet.
• It may have saved a lot of confusion if it had been stated in the beginning that the function was not continuous over the interval [4,6].
• 3.68 doesn't make sense to me, given the definition of a limit. Since the limit is the value that a function approaches, how could we say that it is equal to 3.68 in this case, since we are no longer approaching that value when x gets really close to 5? The function already takes on a value of 3.68, according to the table, so we must be approaching a value that is different, right?
• We aren't claiming that 3.68 is the limit of the function, only that's that is the most reasonable guess among the given choices. In reality, the limit could be anything at all, or may not exist, but the task at hand is to make a reasonable guess from partial information.
• I thought at the limit there would be no value, it would be undefinied. So when the limit goes to 5, and g(x) is 6.37 in this problem, doesn't that mean the limit doesn't exist?
• The question reads: What is a reasonable estimate for the limit of 𝑔(𝑥) as 𝑥 approaches 5?

So, loosely speaking, we are looking for some value 𝐿 (the limit), such that when 𝑥 gets very, very close to 5 (without actually being equal to 5), then 𝑔(𝑥) gets very, very close to 𝐿.

Looking at the table we see that as 𝑥 goes from 4 to 4.999, 𝑔(𝑥) increases and gets closer and closer to 3.68 .
And, as 𝑥 goes from 6 to 5.001, 𝑔(𝑥) decreases and gets closer and closer to 3.68 .

Thereby it is reasonable to assume that the limit of 𝑔(𝑥) as 𝑥 approaches 5 does exist, and that it's value is 3.68 .
• Well in n the graph plotted in most of the questions,test,examples has two different points marked 1) A closed (solid) dot means the endpoint is included in the curve and 2)an open dot means it isn't ...My doubt is if it is the open dot then how does the answer here turn out to 3.68
• Since in question, it is asked "What g(x) approaching as x approaches 5?" When we check for limit from left hand side (i.e., values less than 5) for x = 4.999 (which is very close to 5) we get g(x) = 3.68. Similarly, if we check for limit from right hand side (values that greater than 5), for x = 5.001 we get g(x) = 3.68. So, limit from RHS and LHS are equal, therefore limit for g(x) as x approaches 5 is 3.68.

It does matter if g(x) is different at x = 5 or in your words there is open dot (or for sake of discussion, lets say undefined) because in question we not asked for value of g(x) at x=5 but what we g(x) is approaching as x approaches 5.
• I really don't get it...So why the answer shouldn't be 6.37??Isn't it the really correct answer for the limit?
• The limit at a certain point is the value, that the function seems to be approaching from both sides.
In this case you can see at minute , that the y-value the function approaches, when x=5, is approximately 3.8.
Yes, the real value of g(x) at 5 is 6.37, but that isn't what the lines of the function seem to approach.

Remember, the limit of f(x) at a given point doesn't always equal the value of f(x) at that point, because a limit describes the behavior of functions (what number they are approaching or getting closer and closer to).

You can also estimate the limit from the table, when x equals 5, g(x) is 6.37, but if you look at the rest of values (from above and from the bottom) you will notice a pattern, for example, from x=4 to x=4.999, the g(x) values get closer and closer to 3.68, the same goes for the values below, from x=6 to x=5.01, the values approach 3.68. And when _x_ equals 5, you'd expect the y-value to be somewhere near 3.8, but no, it falls far apart (6.37), but the tendency of the overall function is to approach (get closer to) 3.68, even thought it never reaches that point.
• Why using tables instead of graphs for limits? What are the advantages.
• this is just another method. in the future there will be more.
• Do we disregard the solid point on the graph?