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Video transcript

do some practice examples from our intro to slope y-intercept exercise what is the slope of y is equal to negative 4x minus 3 so you might already recognize this is in slope-intercept form just as a reminder slope-intercept form is y is equal to MX plus b where the coefficient on this X term right over here that is our slope and then this constant right over here that is going to give you your y-intercept so they're saying what is the slope here well I just need to figure out what is the coefficient on this X term and you can see that the coefficient here is a negative 4 so that is going to be our M that is going to be our slope now just as a reminder you have to make sure that it's solved in this way that it is solved for y y is equal to something times X minus 3 so that's our slope let's do another one of these so we're asked what is the y-intercept of y is equal to negative 3x minus 2 so once again we already have it in slope intercept form it's already been solved for y some of the form y is equal to MX plus B where m our slope is given right over here negative 3 but they're not asking for our slope they're asking for the y-intercept well the y-intercept is given by B here so B is negative to play pay close attention to the sign here so B is equal to negative 2 but when I look at these choices I don't see a B is equal to negative 2 so what are they talking about well the y-intercept is what is the Y value when X is equal to 0 and you can see that here X was equal to 0 then that term goes away and Y is equal to B so if you want to know the point where the graph described by this equation intercepts the y axis well it's going to be what what is y when x is equal to 0 well when X is equal to 0 Y is equal to negative 2 and you can see that in our original again if X was zero this term would go away and Y would be equal to negative 2 so 0 comma negative 2 so it would be that choice right over there on Khan Academy obviously just have to click on that you don't have to shade it in let's do one more complete the equation of the line whose slope is 5 and y-intercept is 0 comma 4 so once again the general form is y is equal to our slope times X I want to put in slope intercept form plus our y-intercept well they're telling us our slope is 5 whose slope is 5 so we know that M is going to be 5 and they tell us that the y-intercept is 0 4 so the y-intercept B that is the value of y when x is equal to 0 so the value of y when x equals 0 is this 4 right over here so that is going to be 4 so I could say Y is equal to 5 times X plus 4 and when you're actually entering it on Khan Academy you would just type it in or if you're using the app you would use it with your finger and I always make the mistake of writing y equals and I type in y equals 5x plus 4 notice she already gave you the y equals right over there but that's all you have to do recognize the slope the y-intercept and then remember what the slope-intercept form actually is