Mikeyy1992
Help? Please and thank you! What is the y coordinate of the y−intercept of the line that passes through the points
(−3, −1) and (1, 7)?



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OpenSessame
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3 1
1 7dw:1377494318035:dw

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You have to find the slope of the line!

OpenSessame
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Slope is...\[\frac{ RISE }{ RUN }\]

Mikeyy1992
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Lagging is my life.

Mikeyy1992
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would that be equal to 1/2 for slope? or no?

OpenSessame
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Right:)

Mikeyy1992
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Well, what is my question asking for? the y coordinate?

Mikeyy1992
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Little confused..

OpenSessame
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Yes! To find where the line crosses the Y axes!

Mikeyy1992
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2, 0? Random guess. Lol

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\[y – y _{1} = m(x – x _{1})\]

OpenSessame
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Now using that formula I gave you plug in one of the Points that are given and solve for y.

Mikeyy1992
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1 + 7 = m(3 + 1)

Mikeyy1992
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 7*

OpenSessame
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Not exactly...Only use one set of points and plug it into the y and x with a tiny 1...

OpenSessame
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More like...
y+1= M(x+3)

OpenSessame
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And M means slope so plug that in too!

Mikeyy1992
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y + 1 = 1/2(x + 3)

OpenSessame
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Yup, now solve for Y.

Mikeyy1992
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y = 1/2x + 1/2 ?

OpenSessame
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Yes:)

OpenSessame
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This form is call slope intercept form. To find y plug in 0 for X.

Mikeyy1992
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y = 1/2(0) + 1/2 y = 1/2 ?

OpenSessame
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(0,1/2)

Mikeyy1992
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Now, this will be tricky to put in the written response, because fractions turn from 1/2 to 12. Lol. Should I just put 0.5?

OpenSessame
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Wait...before you write it lets check it...cause something doesnt seem right...

Mikeyy1992
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I feel like it should be a whole number, my teacher said it should be for these ones.

OpenSessame
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I think is should be (0,5)...

Mikeyy1992
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@mathstudent55 Maybe they know if we did anything wrong.

OpenSessame
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I figured out!

Mikeyy1992
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@Luigi0210

OpenSessame
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The slope is 2!

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we have to redo that with the slope of 2.

OpenSessame
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Because its Y/X not X/Y.

Mikeyy1992
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OpenStudy is lagging for me.

OpenSessame
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Its okay! it is (0,5)

OpenSessame
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\[y+1=2(x+3)\]

OpenSessame
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\[y=2x+5\]

Mikeyy1992
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@Luigi0210 I really need to know if he's right. I'm so confused.

OpenSessame
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Sorry for confusing you...:(


Mikeyy1992
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Only if OpenStudy was a real person...

Luigi0210
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So you're just looking for the ycoordinate of the y intercept?

Mikeyy1992
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Yes.

Luigi0210
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Well you know that the yintercept is when x=0 right?

Mikeyy1992
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Yes, but now I don't even know what the slope is anymore. 1/2 or 2 or 5 lol.

Luigi0210
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Slope is:
\[m=\frac{y2y1}{x2x1}\]

Mikeyy1992
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3, 1 1, 7

Mikeyy1992
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1  7

3  1 ?

Luigi0210
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Just plug them in and solve.
and either way works, you get the same answer

Mikeyy1992
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8

4 ?

Luigi0210
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Yup, making the slope 2.
Now we plug that information into the pointslope formula:
yy1=m(xx1)

Luigi0210
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Open was right so far, except for the slope

Mikeyy1992
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y  1 = 2(x  7) ?

Luigi0210
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Yea, not just distribute.

Luigi0210
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*now

Mikeyy1992
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y = 2x  13?

Luigi0210
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Yup!

Mikeyy1992
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Now what?

Luigi0210
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Now we find the yintercept
Meaning that we plug in where ever there is an x. This will give us the y value we are looking for.

Luigi0210
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*0

Mikeyy1992
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What do we use for x? What number?

Mikeyy1992
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0 = 2x  3?

Mikeyy1992
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13......let me type please OpenStudy please...

Luigi0210
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Ah, plug 0 in for x, not y

Mikeyy1992
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y = 2(0)  13 y = 13?

Luigi0210
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Yup, and that's it Mikeyy :)

Mikeyy1992
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I feel like that would be one weird yintercept from where the two dots are on a graph..

Luigi0210
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Your ordered pair is (13, 0)

Luigi0210
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*(0, 13)

Mikeyy1992
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Alright thanks :P

Luigi0210
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Mikeyy..

Mikeyy1992
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Yes?

Mikeyy1992
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Lol. Answer wasn't 13 but I still got a 88. and I have a chance to get a 90 with my written response...

Luigi0210
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Yes I was about to say that.. sorry buddy :(
I just realized that we used the wrong points for the pointslope formula.

Luigi0210
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The answer was actually (0, 5) and the equation was y=2x+5

Mikeyy1992
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It's fine. I had to get over a 60 and I did. So, I'm happy. I need to get off OP before it screws me another time. thanks again

Luigi0210
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Alright, and you're welcome :)