re: Lunch thread: I’ll paypal you $5 if you can tell me what’s wrong with my math-solved

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Ok I have a big paper soon so I’ll hit you up then

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She won't be working too hard to help you with English.

-15x -15y -z = -17
-9x -25y -2z = 51
12x +15y +z = 2

Multiply 1 and 2 by -1 just for convenience:
15x +15y +z = 17
9x +25y +2z = -51
12x +15y +z = 2

Subtract 3 from 1
15x +15y +z = 17
-12x -15y -z = -2

yields:
3x = 15
x = 5

Plug in x and now our equations become:

75 +15y +z = 17
45 +25y +2z = -51
60 +15y +z = 2

Subtract the new 1 from the new 2:
-75 -15y -z = -17
45 +25y +2z = -51

yields:
-30 +10y +z = -68
10y +z = -38
z = -38 -10y <- Call this equation A

Plug A into 1:
75 +15y +(-38 -10y) = 17
75 +15y -38 -10y = 17
75 -38 +5y = 17

37 +5y = 17
5y = -20
y = -4

Since we know x= 5 and y = -4, plug into any of the three to get z, I'll use equation 1:

15x + 15y + z = 17
z = 17 -15x -15y
z = 17 -15(x+y)
z = 17 -15(1)
z = 2

x=5, y=-4, z=2.

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Does this sort of thing have any real world implication?

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Yes. Simultaneous linear equations are used all the time in product pricing, economic theory, physics, probably many other places as well. Back when I was learning this Exxon had a gigantic system of linear equations they would update daily to figure out how much of each petroleum distillate to make in order to maximize profits.

If you add the last row to the first, you get -3x=-15, which immediately tells you x=5, from there use row operations for the rest.

X=5, y=-4, z=2

You write like a chick.....

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is this something you use with any regularity?

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I do, but only because I do a lot of statics, and its quicker for me to do it by hand than run it through a program in most instances.

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Does this sort of thing have any real world implication?

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It has tons of real world applications.

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When I was a struggling undergrad I tutored stuff like this (paid a hell of a lot better than fast food) and ran across quite a few people who said stuff like that. Most of them had never taken a class where problems were asked in English and you had to translate it to an equation. They never had to make the connection between math and the real world.

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"The masses of men lead lives of quiet desperation."

Doesn't really have any relevance to the current stream of thought, but I like the bleakness it projects.

Beer 1 of the day.

Way to whore out the lunch thread for your homework help.

Chicken and rice. Bout to go hack golf ball around in a field for a while

you can do online tutoring for chegg but you have access to solutions manuals and any other questions that other students have asked. Asking for a solution is different than tutoring. You get to ask 30 questions a week and they have folks standing by to answer questions. I make a good bit of side cash doing it. It helps me with classes I don't feel like busting arse with. Chegg is way better than wyzant if you just want the answer to one question