Algebra (all content)
How to graph on a number line and coordinate plane. Created by Sal Khan and Monterey Institute for Technology and Education.
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- when sal shows that no matter what x is, y is always going to be greater than 5, how can you tell why he knows :?(3 votes)
The equation y>5 is a linear inequality equation.
Let's first talk about the linear equation, y=5
If you wrote the linear equation in the form of y=Ax+B, the equation would be
y=0x + 5.
When x=1, what is y? y=5
And when x = 2, what is y? y=5
So no matter what x is, y=5
So whatever we put in for x, we get x*0 which always = 0. So for whatever x we use, y always equals 5.
The same thing is true for y>5.
It could be rewritten as
y > 0x + 5.
And again, no matter what x we use, y is always greater than 5.
I hope something I said here helps it click for you.(53 votes)
- what happens if you have an equation like " 4x < 32" ? How do you answer it and graph it?(13 votes)
- The y-value will be infinite, so just raw a vertical line crossing the point (4,0) and shade away from zero. This way , ANY y-value can work.(9 votes)
- At1:39what does Sal mean by this?(6 votes)
- Can you recommend a video that doesn’t talk about a number line but only how to solve the equation on a graph? Thanks.(3 votes)
- The are 48 learners in a classroom. Two bought a cake a cut into 13 pieces. Express the number of learners in ratio who did not get cake.(3 votes)
- this isn't in the video but how would you solve a problem where there is like kids and adults going to a play and the tickets are different costs and they have to get a certain amount of money??(3 votes)
We're asked to represent the inequality y is greater than 5 on a number line and on the coordinate plane. Let's do the number line first. Let me just draw out a number line. That's my number line, all the possible values of y. Let's make that 0 on the number line. We could obviously go into negative numbers, but we're going to be greater than 5, so I'll focus on the positive side. So let's say that's 1, 2, 3, 4, 5, and then 6, 7, so forth and so on. This number line represents y, and y is going to be greater than 5, not greater than or equal to. So we're not going to be including 5 in the numbers that can be y. So we're not going to include 5, so we're going to do an open circle around 5, and all of the other values greater than 5 will be included. So if there was a greater than or equal to sign, we would have filled it in, but since it's just greater than, we're not including the 5. So we've represented it on the number line. Let's do the same thing on the coordinate plane. Let me draw a coordinate plane here. I'm just using the standard convention. That is my y-axis right there. And then the horizontal axis, I'll just assume is my x-axis. Let me draw some y values, positive y values. 1, 2, 3, 4, 5. That is 5 right there, and you go 6, 7, you can just keep going into larger and larger numbers. And we want y to be greater than 5, so it's not going to be greater than or equal to. So we're not going to include 5. So at 5, at y is equal to 5, we will draw a dotted line. That shows that we're not including y is equal to 5, but we want include all of the other values greater than 5. So that we will shade in. So here we have shaded in all of the values greater than 5. If it was greater than or equal to 5, we would have drawn a bold line over here. So no matter what x is, no matter what x we pick, y is going to be greater than 5.