6x + 4y = 14
2x + 8y = 21
multiply 1st equation by 2, then subtract 2nd:
12x + 8y = 28
2x + 8y = 21
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10x = 7
x = 7/10
start over, multiply 2nd equation by 3 and subtract from 1st:
6x + 4y = 21
6x + 24y = 63
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..... -20y = -42
y = 21/10
2007-11-19 16:25:24
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answer #1
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answered by Philo 7
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I think I remember doing these :)
Multiply the top equation by two, so the y's cancel out, like so:
6x+4y=14 x2
2x+8y=21
12x+8y=28
2x+8y=21
Then subtract the second equation from the first:
12x+8y=28
- 2x+8y=21
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10x = 7
Then simplify:
x= 7/10 or x = .7
Then put this value for x into the equations to find y.
6(.7)+4y=14
4.2+4y=14
4y=14-4.2
4y=9.8
y=9.8/4
y=2.45
Then put both values into the second equation to make sure they are correct. I am to lazy to write this out, but I did them on my calc and they are. Good luck with the rest of your algebra!
Oh, and if you need the answers to be fractions, and you have a TI-83 calculator, you can change them by typing in the number, hitting ENTER, then MATH, then 1 (Frac). You can go from fraction to decimal by hitting 2 (Dec) under MATH.
2007-11-20 00:38:37
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answer #2
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answered by dardianne 2
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Values of y:
6x + 4y = 14
3x + 2y = 7
2y = 7 - 3x
y = (7 - 3x)/2
2x + 8y = 21
8y = 21 - 2x
y = (21 - 2x)/8
Value of x:
8(7 - 3x) = 2(21 - 2x)
4(7 - 3x) = 21 - 3x
7 - 3x = 5.25 - 0.75x
2.25x = 1.75
x = 7/9
Value of y:
= (7 - 3[7/9])/2
= (7 - 7/3)/2
= (21/3 - 7/3)/2
= (14/3)/2
= 7/3
Answer: x = 7/9, y = 7/3 or 2 1/3
Proof:
6(7/9) + 4(7/3) = 14
14/3 + 28/3 = 14
42/3 = 14
14 = 14
2007-11-20 03:35:16
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answer #3
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answered by Jun Agruda 7
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