Algebra

Solve this system of linear equations.

* Used the substitution method

3x - y = 8
4x - y = -15

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WORK

y = 3x - 8

4x - (3x - 8 ) = -15
4x - 3x + 8 = -15
x + 8 = -15
x = -7

3x - y = 8
3(-7) - y = 8
-21 - y = 8
-y = 29
y = -29

The solution of this linear equation is [ -7 , -29 ]

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  1. from your
    x + 8 = -15
    x = -15-8
    x = -23

    then
    y = 3x-8
    = 3(-23) - 8
    = -77

    check:
    in #1
    3x - y
    = 3(-23) -(-77)
    = -69 + 77 = 8 , check!
    in #2:
    4x - y
    = 4(-23) - (-77)
    = -92 + 77
    = -15 , check!

    x = -23 , y = -77

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  2. Can you please explain this? I don't quite understand it.

    from your
    x + 8 = -15
    x = -15-8
    x = -23

    Thanks!

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  3. To get x alone on one side, you have to subtract 8 from both sides.

    x + 8 - 8 = -15 - 8

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  4. Thank you

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    2. 👎

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