anonymous
  • anonymous
I have a question about the slope.... In the slope formula y=mx+b what is the difference between the y and the b and how do I know when to plug it in to the y or b?
Mathematics
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jamiebookeater
  • jamiebookeater
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Nnesha
  • Nnesha
b is y-intercept a point where line cross y-axis(there would be only one ) y = just y-coordinate you don't need to plug anything for y
anonymous
  • anonymous
Example problem: Line A has slope of -5/3 and passes through the point (-2,7). WHat is the x-intercept of line A?
Nnesha
  • Nnesha
yes y=mx+b so replace m with -5/3 y=-5/3x+b now you have x y value (-2,7) x=-2 y=7 substitute x and y for their solve for b(y-intercept )

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anonymous
  • anonymous
I just don't understand what to plug into the y or b.... like if they ask it passes through the line then what do i do? use it for the y or b?
Nnesha
  • Nnesha
x-intercept is a point where line cross the x-axis when y =0 after you find y-intercept substitute y for 0
anonymous
  • anonymous
Like what are some examples of when i have to use it for y or b? what do they have to say for me to know where to replace it?
Nnesha
  • Nnesha
when they say passes through the points (x,y) then you have to find b
anonymous
  • anonymous
so replace the b with the number they say it passes through the points?
anonymous
  • anonymous
or the y
Nnesha
  • Nnesha
replace with y not b (b is y-intercept )
anonymous
  • anonymous
hmmm okay
Nnesha
  • Nnesha
here is an example slope =2 passes through (4,3) \[\huge\rm \color{reD}{y}=mx+b\]\[(4,\color{ReD}{3})\]
anonymous
  • anonymous
So in what cases do i replace the b (y-intercept) what kind of problems do they have to ask for
Nnesha
  • Nnesha
then statement would be like this slope is 3 and ***Y-INTERCEPT =5
Nnesha
  • Nnesha
they would use the *y-intercept ) word
anonymous
  • anonymous
hmmm okay
phi
  • phi
maybe this helps??: y = 3x + 2 is a formula to "find y" if you are told x. you then put the x and y together as a package (x,y) for example, if x is 1, y will be 5 (do you see how?) and (1,5) is the "package" which is just a way to say the point (1,5) is on the line. does that part make any sense?
phi
  • phi
the next idea is we can (in theory) find all the points on the line using its formula that can be useful and the reason we want a formula rather than a long boring list of (x,y) pairs
anonymous
  • anonymous
hmmmm i mean thats easy i'm just hving a hard time understand when to substitute the y or b
Nnesha
  • Nnesha
|dw:1439238885626:dw| i know why you r confused but y-intercept is the specific point where line cross the y-axis which is also one of the y value but they will always use the y-intercept word for b
phi
  • phi
you will get the idea... but I want to make sure you got the basic idea the next idea is how do we find the formula for a line? it turns out you need just two points on the line, and there is a way to do that.
anonymous
  • anonymous
what if they don't specifically use the term y-intercept like how will i know to plug what in where?
phi
  • phi
as you know, the formula for a line is y= m x + b where m is the slope and b is the "y-intercept" if you are given two points, they you know how to find the slope, right ?
anonymous
  • anonymous
2 points like (5, 2)? yea then just plug in 5 to x and 2 to b right?
Nnesha
  • Nnesha
when they say given points where (3,5) where first number represent x-coordinate and and 2nd number represent the y-coordinate (NOT y-intercept )
Nnesha
  • Nnesha
y-coordinate =y y-intercept = b
phi
  • phi
**2 points like (5, 2)? *** oooh! no! a point is (x,y) pair. (5,2) is one point. to find it, you go over 5 and up 2 to get to it.
phi
  • phi
two points would be for example (1,3) and (4,4)
anonymous
  • anonymous
so then 3=m(1)+b?
phi
  • phi
yes, you can do that. but the first step is to find m (which we can do) change in y divided by change in x what do you get for m ?
anonymous
  • anonymous
y2-y1/x2-x1
phi
  • phi
yes, and for (1,3) and (4,4) what do you get for m?
anonymous
  • anonymous
1/3
phi
  • phi
ok. now we go back to the equation 3=m(1)+b and put in m= 1/3 3= 1/3 * 1 + b or 3= 1/3 + b sorry about the ugly numbers... but we can solve for b by adding -1/3 to both sides.
phi
  • phi
you get b= 3 - 1/3 or 8/3 notice if we start with y = 1/3 x + b and put in the other point (4,4) 4 = 1/3 * 4 + b 4= 4/3 + b 4- 4/3 = b and b= 12/3 - 4/3 = 8/3 we get the same b
anonymous
  • anonymous
yea i know about that u'll always get the same solution no matter which u plug in
Nnesha
  • Nnesha
\(\color{blue}{\text{Originally Posted by}}\) @yomamabf 2 points like (5, 2)? yea then just plug in 5 to x and 2 to b right? \(\color{blue}{\text{End of Quote}}\) also when the statement is *passes through point * that means solve for b easy way to memorize it ;)
phi
  • phi
if you are given two points, you find the equation of the line by 1) find the slope 2) use either (x,y) pair to replace the x and y in the equation with numbers and solve for b does that sound ok?
phi
  • phi
if you are told the y-intercept is 3 (for example) that is the same info as telling you that (0,3) is a point on the line (y-intercept is the y value when x is 0)
anonymous
  • anonymous
hmmm okay got it
phi
  • phi
say the problem was: slope is 3 y intercept is 3 what is the equation? two ways to do it: y = mx + b we are told m is 3, so y= 3x + b (0,3) is a point on the line 3= 3*0 + b 3 = b so y= 3x+3 the other way: replace m with 3 (the slope), and replace b with 3 (the y-intercept) y = 3x+3
anonymous
  • anonymous
yea i was thinking the latter
phi
  • phi
yes, but it is good to see how to do it the first way. It always helps to see problems solved in different ways.
anonymous
  • anonymous
hmmm okay got it
anonymous
  • anonymous
thank you!!!!
phi
  • phi
the first way is how you do it for any point on the line. (0,3) is just an easy point (because it tells us what b is ... or multiplying x by 0 is easy)
anonymous
  • anonymous
okay i'm going to try to find another problem and see if i can do it by myself i need practice =(
phi
  • phi
if you get lost, post the problem

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