# 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. 👎
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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2. 👎
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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2. 👎
4. Thank you

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2. 👎

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