How do you solve x+y=1 and 2x−y=−2 using substitution?

1 Answer
Alexander
Jul 10, 2016

By eliminating x in the expression x+y=1, we get

x=1−y, which we can plug in the second expression:

2(1−y)−y=−2

2−2y−y=−2

2−3y=−2

−3y+2=−2

−3y=−4

y=43

Knowing y, we can now find x by plugging the y-value into any of the above equations. For example, by plugging y=4 into the first equation, x+y=1, we get

x+43=1

x=−13

Explanation:

We can check whether these values satisfy the equations by plugging them back in:

First: x+y=1

−13+43=1→43−13=1→12−39=1→99=1

Second: 2x−y=−2

2(−13)−43=−2→−23−43=−2→−189=−2

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