:( I failed

I'm pretty much a math guy. It was always that one class that no matter how bad I felt or how little I listened in class, I could always at least pull a B.

So I feel really bad now because my sister asked for my help on a math problem and for the life of me, I couldn't remember how to do it.

I'll lay it out for you. The teacher does not teach from the book, and makes up the problems. And what is in the book is like this

3y + 4x = 9
59x - 1y = -3

find x and y

I can solve crap like that all day. I can do that sort of stuff with out thought. I can even do that sort of stuff with three variables and with three equations. The problem is the teacher gave something like this for my sister to do.

-5a + 9b -4c -6d = 7
6a - 4b -6c -3d = -9
2a + 7b -5c -d = 1
9a - 2b -6c + d = 0

=/ I just can't remember the order of operations, or how to solve it with one of those gay matrix things. God I hate those things. They only pop up at the end of homework so your teacher can own you.

"How do I do this last problem"
"Oh you have to use a matrix?"
"what?"
"A matrix, you know you were taught those in highschool"
"-_- yeah, maybe THREE fucking years ago"
*teachers solves problem with matrix, you feel like a dumbass*

Anyone else had something like this happen to them, where they forget some nitpicky thing that could help someone else?

It is just flat out frustrating, I’ve had over 10 hours of calc in college and took every advance math class my highschool had, I SHOULD REMEMBER THIS.

>_<

In the words of Group X: "Well, fuck that."

just look up "system of equations matrix" on google. It's really easy. You can find matrix calculators on the web which will verify your answer as well.

Could have been worse, IP. Just imagine what would have happened if she'd asked for help with her English homework!

holy shit... I've forgotten how to do all of those.... in the 4y + 7x = blah blah ones, didn't you have to isolate one variable on a particular side of the equal sign? Damn, its been years since I've had a math class but I still can't believe I dont remember that shit. :(

I somewhat remember the matrices stuff, I may still have some notes on that and the rest of that stuff... i hope, I wonder if I threw all the stuff away.

Quote:

---

Originally Posted by g0zen

Could have been worse, IP. Just imagine what would have happened if she'd asked for help with her English homework!

---

Nice

You don't need a matrix. Just find a lose end and start pulling from there until it unravels. I gave it a shot, but I had a calculation error in there somewhere so the final answers are wrong. No, I'm not going to look for it. Here's the technique tho'.

-5a + 9b -4c -6d = 7
6a - 4b -6c -3d = -9
2a + 7b -5c -d = 1
9a - 2b -6c + d = 0


9a = 2b + 6c - d
a = (2/9)b + (2/3)c - (1/9)d


2[(2/9)b + (2/3)c - (1/9)d] + 7b - 5c -d = 1
(4/9)b + (4/3)c - (2/9)d + 7b - 5c -d = 1
(67/9)b - (11/3)c + (7/9)d = 1
(67/9)b = 1 + (11/3)c - (7/9)d
b = (9/67) + (99/201)c - (7/67)d

6{(2/9)[(9/67) + (99/201)c - (7/67)d] + (2/3)c - (1/9)d} - 4[(9/67) + (99/201)c - (7/67)d] - 6c - 3d = -9
(12/67) + (1188/1809)c - (84/603)d + 4c - (2/3)d - (36/67) + (396/201)c - (28/67)d - 6c - 3d = -9
-(24/67) - 1.37c - 3.95d = -9
-1.37c = -8.64 + 3.95d
c = 6.31 - 2.88d

b = 0.13 + 0.49(6.31 - 2.88d) - 0.1d
b = 0.13 + 3.09 - 0.14d - 0.1d
b = 3.22 - 0.24d

a = .22(3.22 - 0.24d) + 0.67(6.31 - 2.88d) - .11d
a = 0.71 - 0.01d + 4.23 - 1.93d - 0.11d
a = 4.94 - 2.05d

-5(4.94 - 2.05d) + 9(3.22 - 0.24d) - 4(6.31 - 2.88d) - 6d = 7
-24.7 + 10.25d + 28.98 - 2.16d - 25.24 + 11.52d - 6d = 7
-20.96 + 13.61d = 7
13.61d = -0.33

d = -0.02
a = 4.98
b = 3.22
c = 6.37

yeah and a matrix is about 100 times easier, which is why everyone uses them once you get beyond 3 equations.

Damnit, I couldn't remember how to do a matrix. :bang:

Isn't that when things slow down and you bend backwards to dodge stuff?