You can look at that visually there or you can use this formula same exact idea, our ending x-value, our ending x-value is 5 and our starting x-value is negative 1. So it takes us one to go to zero and then five more. So we started at x is equal to negative 1, and we go all the way to x is equal to 5. We started at x is equal to negative 1 and we go all the way to x is equal to 5. Now we just have to find our change in x. And all it does is tell us the change in y you go from this point to that point We have to go down, our rise is negative we have to go down 10. This right here is y2, our ending y and this is our beginning y This is y1. or if you just want to use this formula here it will give you the same thing We finished at negative 4, we finished at negative 4 and from that we want to subtract, we want to subtract 6. And we go down all the way to y is equal to negative 4 So this is rigth here, that is our change in y You can look at the graph and say, oh, if I start at 6 and I go to negative 4 I went down 10. So what is our change in y? So our change in y, to go we started at y is equal to six, we started at y is equal to 6. So let's just make this over here our starting point and make that our ending point. And you just have to pick one of these as the starting point and one as the ending point. This is the same exact thing as change in y and that over the x value of your ending point minus the x-value of your starting point This is the exact same thing as change in x. So this is equal to change in y over change in x wich is the same thing as rise over run wich is the same thing as the y-value of your ending point minus the y-value of your starting point. Or, we can view it as the y value of our end point minus the y value of our starting point over the x-value of our end point minus the x-value of our starting point. So m, or the slope is the change in y over the change in x. This is the slope-intercept form where m is the slope and b is the y-intercept. Remember, we want, we can find the equation y is equal to mx plus b. So good place to start is we can find its slope. So the line will looks something like that. I will draw a dotted line maybe Easier do dotted line. So the line connects them will looks something like this. And we go down 4, So 1, 2, 3, 4 So it's right over there. So it's this point, rigth over there, it's (-1, 6). And the first point is (-1,6) So (-1, 6). And you don't have to draw it to do this problem but it always help to visualize That is my y axis. What is the equation of the line? Let's just try to visualize this. This means that it is an ENTIRELY different point on the line, as the change in y over change in x is equal to -10/6, or -5/3.Ī line goes through the points (-1, 6) and (5, -4). 69/15 = x And lastly, dividing -69 by 15 gives us.Īlright, so we know that when y is equal to -10, then x is equal to -4.6. 23/3 * 3/5 = x And multiplying this out will give us. 23/3 / 5/3 = x As for the left hand side, we know that dividing by a fraction is the same thing as multiplying by it's reciprocal, so it becomes 23/3 / 5/3 = 5/3x / 5/3 The right hand side cancels out 23/3 = 5/3x, so now we divide both sides by 5/3 So first, we subtract 13/3 from both sides. 10 = 5/3x + 13/3 and from this, we can solve for x in this situation. Now to compare this to when y equal to -10, we would have this: We also know from the given points that when y equals 6, x is equal to -1. The change in y over the change in x equals out to -10/6, or -5/3. This is seen when you compare the points and the slope. However if Sal were to use -10, the x value he would have to be different. If -10 from the slope were to be a valid option for a point in this equation, that means that the change in x would also have to be the accompanying point on the line to go with the change in y. He could not use -10, because -10 isn't necessarily a point on the line, because it's the change in y. He used 6 because it was one of the points for y on the line.
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