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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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  • leaf green style avatar for user worldsage
    What's the difference between geometric sequences and exponential functions?
    (23 votes)
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  • starky sapling style avatar for user Nairs
    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?
    (4 votes)
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    • winston baby style avatar for user Jonathan
      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.
      (19 votes)
  • leaf red style avatar for user Hann
    I'm confused. Isn't Exponential Function as same as Geometric Sequence?
    (7 votes)
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    • blobby green style avatar for user e.b.morran
      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.
      (6 votes)
  • piceratops sapling style avatar for user Eliza
    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.
    (5 votes)
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    • primosaur seed style avatar for user Ian Pulizzotto
      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.
      (2 votes)
  • mr pants purple style avatar for user Gilbert
    How is the exponential relationship not a different version of a linear relationship?
    (5 votes)
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    • stelly blue style avatar for user Kim Seidel
      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.
      (4 votes)
  • aqualine ultimate style avatar for user Julian Cofield
    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.
    (1 vote)
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    • starky ultimate style avatar for user KLaudano
      Linear growth is constant. Exponential growth is proportional to the current value that is growing, so the larger the value is, the faster it grows. Logarithmic growth is the opposite of exponential growth, it grows slower the larger the number is.
      (6 votes)
  • duskpin ultimate style avatar for user Rabi
    Hi , I was wondering if there is any relation between linear growth / exponential growth and the arithmetic/ geometric sequences ?
    since exponential is the multiplication of the same number isn't that the same as the geometric sequence ?
    Thanks !
    (2 votes)
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    • primosaur seed style avatar for user Ian Pulizzotto
      Good thinking! The answer is yes. An arithmetic sequence can be thought of as a linear function defined on the positive integers, and a geometric sequence can be thought of as an exponential function defined on the positive integers. In either situation, the function can be thought of as f(n) = the nth term of the sequence.
      (2 votes)
  • aqualine ultimate style avatar for user Brian
    What would a neither relationship look like?
    (2 votes)
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    • duskpin tree style avatar for user esosister
      x: 2 4 6 8
      y: 4 9 16 25
      I'm not sure exactly how to insert a table, but a neither relationship would look something like this. x is increasing by a variable of 2, while y is increasing in no order whatsoever. First it increases by 5, then 7, then 8, so it's neither linear nor exponential.
      (2 votes)
  • blobby green style avatar for user aahumada4466
    Does it still count as an exponential if you are subtracting or diving by a constant number, or would that be linear.

    here are the tables I am referring to :
    x | -1 | 0 | 2 |
    y | 16 | 8 | 4 | ? | y=?
    ________________________
    x | -2 | 0 | 2 |
    y | 8 | 5 | 2 | ? | y=?
    (1 vote)
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  • duskpin seed style avatar for user elizaveta.sosedko
    Is exponential when u multiply or is linear when u multiply?
    (1 vote)
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Video transcript

- [Instructor] So I have two different xy relationships being described here. And what I would like to do in this video is figure out whether each of these relationships, whether they are either linear relationships, exponential relationships, or neither. And like always, pause this video and see if you can figure it out yourself. So let's look at this first relationship right over here. And the key way to tell whether we're dealing with a linear, or exponential, or neither relationship, is think about, okay, for given change in x, and you see, each time here, we are increasing x by the same amount. So we're increasing x by three. So given that we're increasing x by a constant amount, by three each time, does y increase by a constant amount? In which case, we would be dealing with a linear relationship. Or is there a constant ratio between successive terms when you increase x by a constant amount. In which case, we would be dealing with an exponential relationship. So let's see. Here we're going from negative two to five. So we are adding seven. When x increases by three, y increases by seven. When x is increasing by three, y increases by seven again. When x increases by three, y increases by seven again. So here, it is clearly a linear relationship. Linear relationship. In fact, you can even, relationship, you could even plot this on a line if you assume that these are samples on a line. You could think even about the slope of that line. For a change in x, for a given change in x, the change in y is always constant. When our change in x is three, our change in y is always seven. So this is clearly a linear relationship. Now let's look at this one. Let's see. Looks like our x's are changing by one each time, so plus one. Now what are y's changing by? Here it changes by two. Then it changes by six. Alright, it's clearly not linear. Then it changes by 18. Clearly not a linear relationship. If this was linear, these would be the same amount, same delta, same change in y for every time, 'cause we have the same change in x. So let's test to see if it's exponential. If it's an exponential, for each of these constant changes in x's, when we increase x by one every time, our ratio of successive y's should be the same. Or another way to think about it is what are we multiplying y by? So to go from one to three, you multiply, you multiply by three. To go from three to nine, you multiply be three. To go from nine to 27, you multiply by three. So in a situation where every time you increase x by a fixed amount, in this case one, and the corresponding y's get multiplied by some fixed amount, then you're dealing with an exponential relationship. Exponential. Exponential relationship right over here.