Stuck

T

Tig27

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Joined
Feb 20, 2012
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7
Hello!

I have to find an equation of the line through points (-2,-4)(-4,-3)

I know the rule is y2-y1/x2-x1. So for those points I got 1 over -2.

So then I have to pick a pair of those, could be either. Then I do the y-y1=m(x-x1)

So I get y-(-4)=-1/2)x-(-2).

I get y+4=-1x-2.

I know the answer is suppose to be f(x)= -1/2 x-5. But I know I am doing something wrong here, and it's a bit frustrating what I did wrong. Can I get a helping hand on where I goofed. I know there is more to it, I have solved other solutions, but when I get to this one, it gets me stuck. For some reason, when there is a 1 or a fraction involved it makes it a bit tricker.
 
I have to find an equation of the line through points (-2,-4)(-4,-3)

I know the rule is y2-y1/x2-x1. So for those points I got 1 over -2.

So then I have to pick a pair of those, could be either. Then I do the y-y1=m(x-x1)

So I get y-(-4)=-1/2)x-(-2).

I get y+4=-1x-2.
Click to expand...

You just need to keep track of your grouping symbols (parentheses). You wrote "y-(-4)=-1/2)x-(-2)", but you needed to write:

y - (-4)=(-1/2)(x - (-2))

y + 4 = (-1/2)(x + 2)

y + 4 = (-1/2)x - 1 (The (-1/2) is times both the x and the 2.)

y = (-1/2)x - 5

Make sense?
 
I did write it as y+4=-1x+2, didn't I?... That is where I get stuck at.. I noticed that you wrote it as "y + 4 = (-1/2)(x + 2)". What happens to that 2 that is suppose to be (x-x1). When I using the distributive property, would that -1 by -x+2? My ordered pair are (-2,-4) and the -2 is my x1, correct? Sorry if this sounds confusing. I get the part where you give each side a -4 that is how we got -5, -1-4 equals to -5. My question is what happens to that 2?(Sorry if I sound like a parrot). I am getting ultra close understanding this, I just want to make sure what I am doing wrong. Thank you again.

wjm11 said:
You just need to keep track of your grouping symbols (parentheses). You wrote "y-(-4)=-1/2)x-(-2)", but you needed to write:

y - (-4)=(-1/2)(x - (-2))

y + 4 = (-1/2)(x + 2)

y + 4 = (-1/2)x - 1 (The (-1/2) is times both the x and the 2.)

y = (-1/2)x - 5

Make sense?
Click to expand...
 
I believe there is another method, and tell me what you(or anybody thinks). I saw the video with the book.

Same problem. (-2,-4)(-4,-3) I get 1/-2

so again, same rules, I will skip and get to the problem.

Y+4=1(X+2)
Y+3=1x+2
-2(y+4)=1x+2
-2y-8=1x+10. Now I add 8 to each side.

So it becomes -2y+1x+10
Now I divide out.

-2y= 1x/-2+10/-2. I get my answer 1/2x-5
-2

f(x)=1/2x-5

The video guide showed me this way, is it the best way?
 
Tig27 said:
I believe there is another method, and tell me what you(or anybody thinks). I saw the video with the book.

Same problem. (-2,-4)(-4,-3) I get 1/-2

so again, same rules, I will skip and get to the problem.

Y+4=1(X+2)
Y+3=1x+2
-2(y+4)=1x+2
-2y-8=1x+10.( that should be a 2 - but next line is correct) Now I add 8 to each side.

So it becomes -2y = 1x+10
Now I divide out.

-2y= 1x/(-2) + 10/(-2). I get my answer 1/2x-5 <<<< Incorrect - you have several sign problem
-2

f(x) = -1/2 * x - 5

The video guide showed me this way, is it the best way?
Click to expand...

You need to be careful about signs of operations.
 
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