# Foo - Where am I going wrong? Math)

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View Full Version : Where am I going wrong? Math)

Tom Stormcrowe
10-10-08, 08:42 PM
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 :eek:

thomson
10-10-08, 09:07 PM
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.

KingTermite
10-10-08, 09:31 PM
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

10-10-08, 09:33 PM
As a visual guide, here is a graph. Above 3, but clearly below 4.

KingTermite beat me to it regarding the math.

Tom Stormcrowe
10-10-08, 09:38 PM
Thanks, I needed a refresher, I guess, as I haven't had to mess with this for a few years.

thomson
10-10-08, 09:45 PM
I thought we weren't supposed to give the answer

jschen
10-10-08, 09:49 PM
Also, check your equation against the original inputs, and you can clearly see that your equation is wrong.

Tom Stormcrowe
10-10-08, 10:09 PM
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.

jschen
10-10-08, 10:11 PM
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.

10-10-08, 10:15 PM
Math! On a Friday night!

Jeeze ...

deraltekluge
10-10-08, 10:41 PM
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.

Tom Stormcrowe
10-10-08, 11:04 PM
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.

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.