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Course: Algebra 1>Unit 12

Lesson 1: Exponential vs. linear growth

Exponential vs. linear growth

For constant increments in x, a linear growth would increase by a constant difference, and an exponential growth would increase by a constant ratio.

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• What's the difference between geometric sequences and exponential functions?
• A sequence would be like a bunch of dots on a graph at all of the natural numbers for x, the exponential function related to that sequence would be like connecting the dots and going back into the negative numbers also. They are related, but not the same.
• When Sal is giving the Exponential Function example, I noticed when he was saying that it increased by 2, then 6, then 18, you could also see that that 2*3=6, 6*3=18, and so on. Is this another way to find out if a given table is exponential or not, or does this work for only a few types of tables?
• The difference between the terms is called a common ratio. In your case, the common ratio is 3, because every time you get from `f(n)` to `f(n+1)` (to get to the next term), you multiply by 3. For instance, 2 times 3 is 6, and 6 times 3 is 18.

So given any table, to check whether the relation is exponential, just divide each term by the one before it. Say your sequence is 5/3, 5, 15, 45, 135, ... Is it exponential?

Here's the table for the sequence:
`` n  | 1 | 2 | 3 | 4 | 5 ----|---|---|---|---|---a(n)|5/3| 5 | 15| 45|135``

Now we divide consecutive terms. 5 divided by 5/3? 3. 15 divided by 5? Also 3. Repeat for every term in the series. If each term is multiplied by the same number (remember, it's called a common ratio) to get to get to the next, we know that the relation is exponential.
• I'm confused. Isn't Exponential Function as same as Geometric Sequence?
• An exponential function is a function where a fixed number is raised to every x. In other words, you pick a number, and each x on the axis is the power that the number is raised to in order to get y. A geometric sequence is a sequence where every x is multiplied by the same, fixed number. f(n^x) is exponential, f(nx) is geometric.
• x 15 16 17 18
y 10 20 40 70
Is the relationship linear, exponential, or neither?

That is a KA test question. Would anyone mind explaining how it is neither exponential or linear? Obviously not linear but how is it not exponential? Would this not look like a parabola if graphed? If it's not exponential, what is it? In a previous vid, Sal used an example and said that the values don't have to be exact and it can still be one or the other.
• Note, first of all, that the x values increase by the same amount each time. However, the y values neither always increase by the same amount nor always grow by the same factor (for example, 40-20 is not equal to 20-10, and also 70/40 is not equal to 20/10). So the relationship is neither linear nor exponential.

The relationship could be quadratic (parabola) because, while the differences between consecutive x values are constant, the differences between consecutive y values (10, 20, 30) are increasing at a constant rate.
• How is the exponential relationship not a different version of a linear relationship?
• A linear relationship has a constant rate of change. If you take any 2 points on a line, the slope found would be the same if you picked a different 2 points from the line. The graph is also a straight line.

An exponential relations grows / reduces on an accelerated basis. The graph will be a curve, not a straight line. You can find the average rate of change (the slope between 2 points), but it would be different from the slope found between another 2 points on the curve.
• what's the difference between an Exponential function and a geometric sequence?
• The equations look the same. The difference is in the acceptable input values and their graphs.

An exponential function accepts any real number as an input value. It's graph is a smooth continuous exponential curve (so no gaps).

A geometric sequence accepts natural numbers as its input values because the input is which term you are finding. If you graph the points created for the geometric sequence, they would fall on the corresponding exponential graph, but there are gaps in between the points.

Hope this helps.
• sup my homies want some stew
• no, i dont want any stew
• Would I be correct in saying that an example of neither Exponential nor Linear relationships would be if it does not increase at any constant/ fixed ratio?
• Exactly right!
• Is there any difference between exponential and linear growth? Is there any difference between logarithmic growth? I would assume that logarithmic growth is similar to exponential growth.