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solve by addition

5x-4y=-5
x-2y=-7

2007-08-17 12:38:39 · 5 answers · asked by blue_eyed_woman_23 3 in Science & Mathematics Mathematics

5 answers

First we have to multiply of the equation to make either the x or y value the same in both equations.

Let's multiply 2 to both sides of the equation
x - 2y = -7

2(x - 2y) = 2(-7)
2x - 4y = -14

So now we stack up the equations

5x - 4y = -5
2x - 4y = -14

We can subtract downwards and

5x - 2x = 3x
(-4y)-(-4y) = 0
-5 - (-14) = 9

so 3x + 0 = 9
3x = 9
x = 3

We plug x = 3 into one of the 2 equations to get the y value

3 - 2y = -7
2y = 10
y = 5

So, x = 3 and y = 5 is the answer

2007-08-17 12:46:11 · answer #1 · answered by kousuke51 2 · 0 0

Write down the equations
(EQ 1) 5x - 4y = -5
(EQ2) x - 2y = -7
Multiply the second equation by 5
(EQ 3) 5x - 10y = -35

Subtract EQ 3 from EQ 1
(EQ 4) 0x +6y = +30

Divide by 6
(EQ 5) y = 30/6 = 5

Plug this value of y back into EQ 2
(EQ 6) x - 2(5) = -7
(EQ 7) x - 10 = -7
(EQ 8) x = -7 + 10 = 3

So the answer is:
x = 3
y = 5

Check:
5x - 4y =? -5
5(3) - 4(5) =? -5
15 - 20 =? =5
-5 =? -5
Yes, so the answer checks.

2007-08-17 19:50:35 · answer #2 · answered by morningfoxnorth 6 · 0 0

Hello

So we have
5x-4y=-5
x-2y=-7

So lets subtract these equations (thus adding negatives).

This is also called the Elmination method. We need to eliminate a variable. Lets multiple the 2nd equation by -5.

So we have
5x-4y=-5
-5(x-2y=-7) = -5x+10y=35

Now lets add these equations:
5x-4y=-5
-5x+10y=35

6y = 30
Thus y=5 and plug this into any equation to get x = 3.

Hope this helps

2007-08-17 19:44:27 · answer #3 · answered by Jeff U 4 · 0 0

5x-4y=-5..........(1)
x-2y=-7..........(2)
By eliminating one of the unknown variables easily the value of the other can be calculated. To do this one of the variables should be made equal.(No matter what sign it is). Let us take "y". By multiplying all the terms in equation (2) by "2" the term of "y" will become 4y. Quantitatively, this is equal to the "y" term in equation (1). To eliminate, addition or subtraction can be done. In the case of "x" if you multiply the equation (2) by "5" the "x" term will become equal.

(2) * 5 = 5x - 10y = -35..........(3)
(3) - (1) = ...... -6y = -30
. . . . . . . . . . . . . . y = -30/-6 = 5
Now, substitute the value of "y" in any one of the given equations. Let us take eqn (2)
x - 2 * 5 = -7
x - 10 . . = -7
x . . . ... . = -7 +10 = 3
Hence, the value of x=3 and the value of y = 5.........Ans.
. .. . . . . . . . .. . . . . . ====================

2007-08-17 20:14:48 · answer #4 · answered by Joymash 6 · 0 0

5x-4y=-5 <-- Eq 1
x-2y=-7 <-- Eq 2
-2x +4y =14 <-- Eq 3 = Eq 2 * -2
3x = 9 <-- Eq3 + Eq 1
x = 3
3-2y = -7
-2y = -10
y = -5

2007-08-17 19:47:09 · answer #5 · answered by ironduke8159 7 · 0 0

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