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Plotting an inequality example

Drawing a number line helps visualize 'x is less than 4'. We mark 4 with a circle, not a dot, because 4 isn't included. Then, we color the line below 4, showing all values less than 4. Easy peasy, lemon squeezy. Created by Sal Khan and Monterey Institute for Technology and Education.

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  • aqualine tree style avatar for user flawabud101
    Hello! Can anyone help me? How do you remember the difference between: ≤ ≥ < > and the open dot and the closed dot. Also, for example, if there's the problem: x ≤ 5 . Here's my questions (P.S.: This all applies to a number line): Which direction should the line go? Should the dot be opened or closed? Is there a way to remember it? Thanks to y'all for answering! Plz try and answer soon! Bye!
    (16 votes)
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    • mr pink green style avatar for user David Severin
      Not sure if you know the signs or not, but one way of thinking about greater than and less than is to make signs with your thumb and pointing finger. If the sign looks like your left hand (<), left is less than. If the sign looks like your right hand (>), Tony the Tiger says right is Grrrrrrrrrrrreater. If you have a line underneath (≥ or ≤) you have to add the phrase or equal to, so ≥ is greater than or eqaul to and ≤ is less than or equal to.
      As far as the open and closed circle, the best way is to understand what it really means. If you were just going to show x=3, you would put a closed dot on 3. So a closed dot means the point counts and you need the equal sign below the line (≥ or ≤). If you have an open circle, the point does not count, thus no equal line. If you have a positive variable on the left, the sign points toward the direction that you draw the line (so x< and x≤ both point toward the left, so start at your point (either open or closed), draw left and end with an arrow <------. If the sign points to the right (> or ≥), then start at point (either open or closed) and draw to the right --------->.
      Does this help, or do you need more?
      (11 votes)
  • mr pink red style avatar for user Walker, Lauren
    when do you close the circle?1!
    (12 votes)
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  • blobby green style avatar for user Gina Marquez
    what does it mean when the dot is open on the 2 and the line is going both negative and positive ways?
    (12 votes)
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  • leafers ultimate style avatar for user Val B.
    For some reason, I cannot remember when to use an open circle, and when to use a solid dot on these number lines.
    (6 votes)
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    • leafers seedling style avatar for user Britt
      I always remember: an open circle is around the number, so it doesn't actually touch the number, meaning it does not include the number itself. A filled in dot is really on the number itself, so that does include the number.
      (13 votes)
  • marcimus red style avatar for user Marcimus
    why do you not stop at dot 3?
    (6 votes)
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  • starky seedling style avatar for user 3209jones
    I Love Math WOOWOO! GO MATH!
    (7 votes)
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  • blobby green style avatar for user David White
    Would it still be x < 4 if you did not put a circle on 4?
    (3 votes)
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    • stelly blue style avatar for user Kim Seidel
      The dot or circle is always used so there is no ambiguity as to where the inequality starts. An open dot tells you that the inequality is "<" or ">" with the arrow's direction telling you which applies. A solid dot tells you that the inequality is ">=" or "<=".
      (7 votes)
  • aqualine ultimate style avatar for user Luke
    How would you graph x=4?
    (5 votes)
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  • starky seedling style avatar for user Matzke
    thanks for help
    (6 votes)
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  • blobby green style avatar for user jacampbell29
    Graph x is less than 4. So let's draw ourselves a number line over here. So let me draw a number line. I'll start here at 0, so 0, 1, 2, 3, 4, 5. And we could go below 0. We'd have negative 1, negative 2, negative 3, negative 4. I could keep going. Now, we want to graph all of the x's that are less than 4, but we're not including 4. It's not less than or equal to 4. It's just less than 4. And to show that we're not going to include 4, what we're going to do is we're going to draw a circle around 4. So this shows us that we're not including 4. If we were including 4, I would make that a solid dot. And to show that we're going to do all the values less than 4, we want to shade in the number line below 4, going down from 4, just like that. And then we can just shade in the arrow just like that. So this right here is all of the values less than 4. And you could test it out. Take any value where there's blue. So there's blue over here, negative 2. Negative 2 is definitely less than 4. If you take this value right here, this 2, it's definitely less than 4. 4 is not included because 4 is not less than 4. It's equal to 4. 5 is not included because 5 is not less than 4.
    (6 votes)
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Video transcript

Graph x is less than 4. So let's draw ourselves a number line over here. So let me draw a number line. I'll start here at 0, so 0, 1, 2, 3, 4, 5. And we could go below 0. We'd have negative 1, negative 2, negative 3, negative 4. I could keep going. Now, we want to graph all of the x's that are less than 4, but we're not including 4. It's not less than or equal to 4. It's just less than 4. And to show that we're not going to include 4, what we're going to do is we're going to draw a circle around 4. So this shows us that we're not including 4. If we were including 4, I would make that a solid dot. And to show that we're going to do all the values less than 4, we want to shade in the number line below 4, going down from 4, just like that. And then we can just shade in the arrow just like that. So this right here is all of the values less than 4. And you could test it out. Take any value where there's blue. So there's blue over here, negative 2. Negative 2 is definitely less than 4. If you take this value right here, this 2, it's definitely less than 4. 4 is not included because 4 is not less than 4. It's equal to 4. 5 is not included because 5 is not less than 4.