Sharpe Posts: 8, Reputation: 1 New Member #1 Jul 5, 2007, 07:18 PM
System of equations
7 x + 4 y = - 2,
10 x - 3 y = 32
I need help with this question.
I am using elimination.
I keep get x=2 but I can't find y.
So I'm guessing that x might be wrong..
But I don't know what I'm doing wrong:confused:
 BIsovski Posts: 2, Reputation: 1 New Member #2 Jul 5, 2007, 07:58 PM
Okay,

There are many ways to solve system equations, or in this case so called 2 equations with 2 unknowns.

Below I provide one method, but I encourage you to find your own method

7 x + 4 y = - 2,
10 x - 3 y = 32

We want to eliminate one unknown and solve for the other.
The common denomitor of 4y and (-) 3y is 12. If we multiply the first equation with 3 we get 12y an the second equation with 4 we get (-) 12y, therefore

(3) 7x + (3) 4y = (3) (-2)
(4) 10x - (4) 3y = (4) 32

from here we get

21x +12y = -6
40x -12y = 128

if we add these to equations we can eliminate the y part

61x = 122 therefore

x = 2

once we have one variable, we can substitute it on either equation to get y

lets take the first original equation
7(2) + 4y = -2, from here
4y = -16 and
y = -4

bwt, these are first order equations.

 Sharpe Posts: 8, Reputation: 1 New Member #3 Jul 5, 2007, 08:06 PM
Thank you!!
 s_cianci Posts: 5,472, Reputation: 760 Uber Member #4 Jul 6, 2007, 05:03 PM
After getting x = 2, just go back to either 7x + 4y = -2 or 10x - 3y = 32, plug the 2 in for x and solve for y.

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