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Post by kazkame on Jul 31, 2007 10:20:49 GMT -5
2x + 5y = 28 x-2y= 2
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Post by Baboon on Jul 31, 2007 10:31:55 GMT -5
Double the bottom to make one variable disappear: 2x + 5y = 28 2x - 4y = 4
Subtract the two lines:
2x + 5y = 28
2x - 4y = 4 0x + 9y = 24
Solve for one variable: y = 24/9 ≈ 2.67
Insert known variable into one of the lines, solve: 2x + 5(24/9) = 28 2x + 40/3 = 28 2x = 44/3 x = 22/3 ≈ 7.33
And, to confirm, stick both known variables into the second line: x-2y= 2 (7.33) - 2(2.67) = 2 7.33 - 5.33 = 2 You shouldn't really convert into decimal, but it's easier to visualize for checking the work.
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Post by kazkame on Jul 31, 2007 10:48:45 GMT -5
thank you babs that one has been killing me all day
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Post by kazkame on Jul 31, 2007 13:57:13 GMT -5
another one ( i'm not good linear equations)
5x-4y = 27 3x+2y = 9
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Post by ch00beh on Jul 31, 2007 14:01:23 GMT -5
double the bottom equation again and subtract. The y variable cancels.
Basically, the easiest way to deal with these is to try to make one of the variables cancel by multiplying / dividing the equations. Kinda like fractions. But not really.
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Post by kazkame on Jul 31, 2007 14:04:20 GMT -5
but i end up with these super ugly fraction that dont work
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Post by Baboon on Jul 31, 2007 14:20:01 GMT -5
Multiply the bottom by -2 to cancel the y's (-4 - -4 = 0) 5x - 4y = 27 -6x - -4y = -18
Subtract: 5x - 4y = 27 -6x - -4y = -18 11x - 0y = 45
Solve for x: 11x = 45 x = 45/11 ≈ 4.09
Put 45/11 in for x, convert 27 into elevenths: 5(45/11) - 4y = 27 -4y + 225/11 = 297/11
Solve for y: -4y = 72/11 y = -18/11 ≈ -1.64
Put x and y into the second line to confirm: 3x+2y = 9 3(45/11) + 2(-18/11) = 9 3 (4.09) + 2(-1.64) = 9 12.27 - 3.27 = 9
Ugly, indeed, but they work out.
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Post by kazkame on Jul 31, 2007 14:24:35 GMT -5
omg i had that an i thought i was wrong ...stupid me
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Post by Baboon on Jul 31, 2007 14:27:59 GMT -5
Yeah, these can get really tangled up. The hardest part about it is deciding by what to multiply one of the lines. Watch any negative signs and you should be fine.
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Post by Kuroboom on Jul 31, 2007 22:43:01 GMT -5
'Cause knowledge is POWER!
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Post by Damien on Aug 1, 2007 7:23:24 GMT -5
This my new favourite game.
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Post by kazkame on Aug 1, 2007 9:22:37 GMT -5
lol pika
x + 2y = 5 2x+4y = 1
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Post by Baboon on Aug 1, 2007 22:39:03 GMT -5
Something here confuses me. Doubling the top results in 2x + 4y = 10 2x + 4y = 1
...Clearly something's not right here.
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Post by Kuroboom on Aug 1, 2007 22:41:21 GMT -5
I wasn't the only one that got that then. I thought I was just rusty as hell.
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Post by ch00beh on Aug 2, 2007 13:00:56 GMT -5
0 = 9
Hooray!
Um, that problem's like unsolveable. Check to make sure you copied it down right. I've done that a lot, which just leads to frustration, which then leads to anger, then hatred, then the darkside. And We Just Can't Have That.
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Post by kazkame on Aug 2, 2007 13:14:29 GMT -5
yup I wrote it out correctly, so i guess it has no solution.
yay
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Post by ch00beh on Aug 2, 2007 13:32:30 GMT -5
when all else fails, ask your teacher.
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Post by kazkame on Aug 2, 2007 15:28:08 GMT -5
all right guys
Factor
3x squared minus 9
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Post by Prof. Cinders on Aug 2, 2007 15:31:12 GMT -5
Is that 3 (x^2) - 9 or (3x)^2 - 9 ?
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Post by kazkame on Aug 2, 2007 15:54:50 GMT -5
(3x ^2) - 9
oh for double points
(4x^2) - 20
Score so far Babs: 2 pts choobs: 1pt Kuro: 0pts Cinders: 0pts
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Post by Prof. Cinders on Aug 2, 2007 16:45:06 GMT -5
(3x)^2 - 9 = 9(x^2) - 9 = x^2 - 1 Therefore x^2 = 1 And x = 1
OR if it's the other way, since you didn't... actually answer my question...
3(x^2) - 9 = x^2 - 3 Therefore x^2 = 3 And x = root-3
If it's only the x that's squared, it's the 2nd one, and if it's both the 3 and the x that's squared, it the 1st.
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Post by ch00beh on Aug 2, 2007 17:33:40 GMT -5
Right. Cinders actually knows math. Pfft.
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Post by Loogs on Aug 4, 2007 9:00:50 GMT -5
I guess I'm disqualified on the grounds of being one grade lesser than Kaz.
Awww, I wanted to have fun with Pre-Calculus. =(
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Post by ch00beh on Aug 4, 2007 11:52:35 GMT -5
Fun with pre-calc?
Pre-calc is soooo boring. Most of the year, I was drawing pies on the back whiteboard. It's all stuff you already know. Sigh.
EDIT: Actually, scratch that, figuring out the sines and cosines of certain values of pi without a calculator was kinda cool. I guess the speed quiz was fun (find the sines and cosines of pi of about 20 problems in less than 5 minutes).
But that's about it. And I enjoy pie. So that's probably why I had fun with those.
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Post by Loogs on Aug 4, 2007 11:56:51 GMT -5
Sarcasm, my dear ch00bs.
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Post by Beelzebibble on Aug 4, 2007 11:58:44 GMT -5
It's them dag-blanged kids and their scar-chasms again! We never used scar-chasms when I was your age!
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