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Old 10-10-08, 07:42 PM   #1
Tom Stormcrowe
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Where am I going wrong? Math)

I can't figure out where I'm going wrong on this.....help please!
Points A(5,0), B(-1,4) a find slope first
M AB=(4-0)/(-1-5)=4/-6, so m=-2/3

y=mx+b
y=-2/3x+4


The school server says the correct answer is y=-2/3x+10/3......

I thought I knew this stuff
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Old 10-10-08, 08:07 PM   #2
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b is the y intercept, that is the y point where the line crosses the y axis.
It is not the difference in y values from two arbitrary points.
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Old 10-10-08, 08:31 PM   #3
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b is the y intercept. Once you have the slope, you can plug either point back in and solve for b.

In the first case:
0 = -2/3(5) + b
0 = -10/3 + b
b=10/3

Use other point to get same result
4 = -2/3(-1) + b
4 - 2/3 = b
12/3 - 2/3 = b
10/3 = b

Either way, you get same y-intercept, so answer is y=-2/3x + 10/3
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Old 10-10-08, 08:33 PM   #4
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As a visual guide, here is a graph. Above 3, but clearly below 4.

KingTermite beat me to it regarding the math.
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Old 10-10-08, 08:38 PM   #5
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Thanks, I needed a refresher, I guess, as I haven't had to mess with this for a few years.
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Old 10-10-08, 08:45 PM   #6
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I thought we weren't supposed to give the answer
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Old 10-10-08, 08:49 PM   #7
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Also, check your equation against the original inputs, and you can clearly see that your equation is wrong.
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Old 10-10-08, 09:09 PM   #8
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Yeah, I was just getting stressed out and frustrated. Not a good combination, if you know what I mean. Forest/trees issue. It was all blurring together in frustration.
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Old 10-10-08, 09:11 PM   #9
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No, not a forest/trees issue. Math is not subject to interpretation. One needs to make sure one's fundamental concepts are rock solid and go from there.
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Old 10-10-08, 09:15 PM   #10
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Math! On a Friday night!

Jeeze ...
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Old 10-10-08, 09:41 PM   #11
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How are you with solving systems of simultaneous equations?

Here's another way of looking at the problem:

You want to write an equation of the form

y = mx + b

You have two sets of values for x and y that will satisfy the equation...plug each set into the equation and get a system of two equations for m and b.

0 = 5m + b
4 = -m + b

Now, solve for m and b.
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Old 10-10-08, 10:04 PM   #12
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Actually, it was, because I had gotten so frustrated I wasn't thinking straight and couldn't even see a glaring error. I took a break, chilled out and went through the rest of the problems with no issues. I'm extremely right brain dominant, and have always had issues with math.

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No, not a forest/trees issue. Math is not subject to interpretation. One needs to make sure one's fundamental concepts are rock solid and go from there.
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