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October 21, 2014

October 21, 2014

Posted by **Kristin** on Saturday, March 13, 2010 at 1:03am.

1)

6m+n=47

m-4n=12

2)

6x+4y=-10

-7x+y=57

3)

5x+7y=43

-4x+y=25

- Math -
**Reiny**, Saturday, March 13, 2010 at 8:06amI use substitution when I notice that in one of the equations one of the variables has a coefficient of 1

Then solve for that single variable

e.g. in #2

-7x + y = 57 ,

y = 7x + 57

now sub that into the other equation

6x + 4y = -10

6x + 4(7x+57) = 10

6x + 28x + 225 = 10

34x = - 218

x = -218/34 = - 109/17

then y = 7(-109/17) + 57

y = 206/17

do the other two the same way

- Math -
**Kristin**, Saturday, March 13, 2010 at 9:52amOkay but the homework is saying the answer is (-7,8) so how would they have gotten that from the equation you did above?

- Math -
**Reiny**, Saturday, March 13, 2010 at 12:04pmI made a transcript error.

After 6x + 4(7x+57) = 10 it should have been

6x + 28x + 228 = -10

I had 2 errors in copying that line, sorry about that

Now i works out

- Math -
**Kristin**, Saturday, March 13, 2010 at 5:11pmOkay so what about number one it is a + and the a - for the second problem how do you figure a subtitution problem like that? do the signs make a difference?

- Math -
**Kristin**, Saturday, March 13, 2010 at 5:16pmFor number 3 I got (6.7,51.8) is this correct?

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