anonymous
  • anonymous
How do I know which is right- y2-y1 over x2-x1 or y1-y2 over x1-x2 People say it's the same on yahoo answers but they get different answers a lot. HELP It's different. Let's say (-2,8) and (2,-1). First way: -1 - 8 = -9 2 - (-2) = 0 So... -9/0 Second way: 8- (-1) = 9 -2 - 2 = 0 So... 9/0 See it's like this all the time. In this example they are the same because it is undefined, but in other examples they are regular numbers that are negatives.
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
anonymous
  • anonymous
Its the same, but in different order.
anonymous
  • anonymous
either one works... so long as your going the same way. point 1 to point 2 or point 2 to point 1
anonymous
  • anonymous
check it out... \[ \frac{y_{2} - y_{1}}{x_{2} - x_{1}}=\frac{-(y_{1} - y_{2})}{-(x_{1} - x_{2})}=\frac{y_{1} - y_{2}}{x_{1} - x_{2}}\]

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Psymon
  • Psymon
If you choose a y1, the x1 better be from the same point. As long as you make x1,y1 the same point and x2,y2 the same point, it really doesnt matter Ex. (3, -4) and (-5,2) So lets make the (-5,2) my point 2 \[\frac{ 2-(-4) }{ -5-3 }=\frac{ -3 }{ 4 } \] Now lets do it the other way, Ill have (3,-4) be my point two: \[\frac{ -4-2 }{ 3-(-5) }=\frac{ -3 }{ 4 }\]
anonymous
  • anonymous
yes... check your arithmetic @Mia_Rachel
anonymous
  • anonymous
What did I do wrong?
Ness9630
  • Ness9630
I think you guys scared her
anonymous
  • anonymous
2-(-2) = 2 + 2 because subtraction is addition of the opposite
Ness9630
  • Ness9630
Psymon and pg scaring users with their math? Not surprising
anonymous
  • anonymous
also, -2 - 2 = -2 +(-2) = -4
anonymous
  • anonymous
what? when did math get scary?
Psymon
  • Psymon
\[\frac{ -1-8 }{ 2-(-2) }=\frac{ -9 }{ 4 } \] \[\frac{ 8-(-1) }{ -2-2 }=\frac{ -9 }{ 4 } \]
anonymous
  • anonymous
challenging, frustrating, down right nasty... but not scary!
Psymon
  • Psymon
I think for a lot of people it gets scary when there are no numbers. Which is kind of ironic.
anonymous
  • anonymous
letters are so much easier to deal with...
anonymous
  • anonymous
I'm sorry it's not (2,-1) it's (-2,-1).
anonymous
  • anonymous
in that case you're dividing by 0, either way you do it. since division by 0 leads to an undefined quotient, the slope is undefined in both cases. you'll learn more about this in calculus when you actually look closer at division by 0.
Psymon
  • Psymon
Well, either way, even though the numbers I used were not the correct numbers, can you see how you still get the same answer if you do the math correct?
anonymous
  • anonymous
Can you do it with the same numbers too? I like to see examples. :/
Psymon
  • Psymon
I gave an example way up above already using numbers I invented.
anonymous
  • anonymous
With the numbers I use please. (-2,8) (-2,-1)
anonymous
  • anonymous
what you did is correct... you get 2 seemingly different answers, but they're not. in both cases you're dividing by 0 which is undefined... meaning both ways actually give you an undefined slope. if you examine the numbers, they have the same x coordinate meaning you have a vertical line. what's the slope of a vertical line?
anonymous
  • anonymous
undefined
Psymon
  • Psymon
Honestly, your example doesnt perfectly show how the signs end up being the same. If one of those -2's were any different number, you would come out with the same answer and you would not have to worry about having the incorrect sign. In your case it's just undefined no matter what, which means a vertical line.
anonymous
  • anonymous
Thanks! Sorry, I just got back to school and I can't remember anything in my math class (Alg II/Trig) and I'm in 9th grade.
anonymous
  • anonymous
But can someone solve it for me? Apparently the answer is x=-2 (back of textbook) but can someone show me step by step how that happens?
anonymous
  • anonymous
exactly... and what is \[\frac{9}{0} \text{ ?}\] what about \[-\frac{9}{0} \text{ ?}\]
anonymous
  • anonymous
they're both undefined, right? like i said, you'll look more closely at this in calculus.
anonymous
  • anonymous
Someone please show me step by step :(
anonymous
  • anonymous
for the whole problem
anonymous
  • anonymous
you already did it Mia... what is giving you trouble?
anonymous
  • anonymous
I mean make up the linear equation with that. I still need to know b (y=mx+b).
anonymous
  • anonymous
check it out... you have a vertical line. they have a special form (as does a horzontal line). for a vertical line, it's x = some number. in your case, x = -2 because no matter what y is, x is always -2.|dw:1378414931060:dw| for a horizontal line, the equation will always be y = some number, for example, y = 5. no matter what x is, y will always be 5 |dw:1378414985808:dw|
anonymous
  • anonymous
I know that, but where did you get the -2?
anonymous
  • anonymous
from the points you gave... (-2, 8) and (-2, -1) see, x is always -2.
anonymous
  • anonymous
OH DUHHHHHHH
anonymous
  • anonymous
lol
anonymous
  • anonymous
But what's the mathematical way you find that?
anonymous
  • anonymous
when you find that the slope is undefined, that's when you know you have a vertical line. then you know the eqution of the line willl be in that form. likewise, when you get a slope of 0, you know you have a horizontal line and that the equation will be y = some number and some number will be the y coordinate of any of your points.
anonymous
  • anonymous
You are a SAVIOR. THANKS I'm done with all of my questions xD
anonymous
  • anonymous
thanks for sticking with it and making sure you understand! you're on your way to being an excellent mathematician!!!
anonymous
  • anonymous
Ahaha thanks, I'm stubborn (:
anonymous
  • anonymous
an excellent quality for anyone who wants to learn and understand ; )

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