Question 1

at 0:58 Sal says delta. Where does this come from?

Accepted Answer

Delta is the fourth letter of the Greek alphabet which is usually used for denoting change between two values. For e.g. Δy means the change or difference between the two values of the y co-ordinates.

Question 2

how do I find the slope  of a triangle

Accepted Answer

Only lines have slope, not shapes. If you want to fund the slope of the sides of triangles, then you'll need to know two coordinate points on the sides and then use the slope formula (change in y)/(change in x).
Example:
There's is a Triangle ABC where A is (0, 0), B is (2, 3), and C is (5, 6). What is the slope of each side of the triangle.
The slope of AB is:
(change in y)__(3-0)
-------------=-----=3/2
(change in x)__(2-0)
The slope of BC is:
(change in y)__(6-3)
-------------=------=1
(change in x)__(5-2)
The slope of AC is:
(change in y)__(6-0)
-------------=-----=6/5
(change in x)__(5-0)

I hope this helps!

Question 3

Hey, How do I know if I am suppose to count the slope over the line or under the line between the two points?

Accepted Answer

You can do either way. One thing, the signs might differ a little when you're doing the sum, but ultimately, after you simplify the answer, you'll see that whichever direction you went, the answer will be the same.
NOTE THIS: If you're going left, it'll be negative.
                   if you're going right, it'll be positive.
                   if you're going downwards, it'll be negative.
                   if you're going upwards, it'll be positive.
if you don't understand this negative - positive thing, you can check out the topic - *Quadrants*.

Question 4

if x = 19y - 3, is 19 the slope? and how do you solve that?

Accepted Answer

It depends on how you look at the problem. Normally mathematicians consider the  xy-plane, it is the coordinate system you are probably most familiar with. Another plane is the yx-plane, then your y-axis is pointing to the left/right and your x-axis up/down. In the xy-plane (the coordinate system) we write a line as y=kx+m. The k in the equation y=kx+m is the slope of the line in the xy-plane (the coordinate system). The m in the equation y=kx+m is where the line hits the y-axis (that's like saying "where x=0"). So, if we put in x=0 we get y=k*0+m=m, so m is the value where the line hits the y-axis, just as I told you!

To solve your problem, we do like this.

We look att your equation x=19y-3, we now that the slope here is 19 and where the line hits the x-axis is where y=0, x=19*0-3=-3, so x=-3 is where the line hits the y-axis. But now we are talking about the yx-plane! Lets think about the xy-plane (the usual coordinate system).

So we have x=19y-3, and we want to solve for y.

x=19y-3
add 3 to both sides
x+3=19y
divide by 19
(x+3)/19=y
simplify
x/19+3/19=y
change the order of the equation
y=x/19+3/19

Now our equation is on the form y=kx+m.

Here k=1/19, because x*(1/19)=x/19

and m=3/19

Question 5

At 1:05 What does the triangle on x+3 stand for?

Accepted Answer

It's not a triangle, it's "delta". In this case it means that you have to find the absolute value of x1 (which is -3) minus x2 (which is 0). The result is 3.

Question 6

I have a question about getting slope from a graph, is there a specific location in the slope that i have to pick or is it any point that intersect with the horizontal and vertical grids? 
Also does the points have to be in one quadrant?

Because i was doing the problems and it seems they don't allow for more than 2 exact points to be the right answer.

Accepted Answer

As long as the line you are measuring the slope of is straight, it will have the same slope everywhere, so it doesn't matter which two points you pick.  They don't have to be in the same quadrant, although it's usually easier to pick two points in the first quadrant if you can, though, because then you all positive coordinates and you're not having to worry about subtracting negatives and so on.  It can also be easier to pick the points where the line intersects the axes, because there one of the coordinates will be zero, which again makes the subtraction easier.  An example:  if the two points on the line are (3,0) and (-1,8) then the slope is (8 - 0) / (-1 - 3) = 8 / (-4) = -2.

Question 7

i have heard of other methods to find slope' what are they?

Accepted Answer

There one way to find slope but there are many shortcuts like  y=mx+b  when mx= slope and +b= y intercept

Question 8

I'm in high school I've got no clue still how to plot a point could anyone give me any evidence on how to understand it better

Accepted Answer

Okay. First let's visualize the coordinate plane (the graph). Going across, we have the x axis. Going up and down we have the y axis. On these axes are numbers. The numbers are spaced evenly. Using these numbers, you can find any point on either of the axes. For example, If I asked you to find 5 on the x axis on the following graph:
```
y axis
|
6
|
4
|
2
|_ 2 _ 4 _ 6 _ 8 _   <----- x axis
```

you would tell me that it is right in between the "4" and the "6" on the x axis. They're just two number lines. Now, to find a point on the plane (that is, a point in the space) you need two numbers: one for it's x location, and one for it's y location. Think of it this way: the x value tells you how far across the point is. If a point has an x value of 4, for example, you know that it is on the number 4 on the x axis, or it is directly above or below the number 4. The same goes for the y value, only this time it tells you how far up the point is.

The only thing we haven't covered is how we notate all of this, and this is quite trivial. If I say point x has coordinates [4,5], that means that it has an x value (or x coordinate) is 4, and the y value (or y coordinate) is 5. On a graph, that would look like this:
```
|
6
|
4
|       .  <== our point is "4 across" (directly above
2                                    number 4) and it is 
|_  2 _ 4 _ 6 _ 8 _      "five up" (directly across from
                                        where the number 5
                                        would be).
```

Question 9

I am really attentive and focusing in class my math teacher told me to come on here for better understanding but i still dont understand can someone please help?

Accepted Answer

Visually, a line has negative slope if it goes down and right (or up and left).  Mathematically, this means that as x increases, y decreases.

8th grade

Course: 8th grade > Unit 3

Slope of a line: negative slope

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