College Algebra / Unit 9 Alg 482 short lesson, about 20 seconds
The Substitution Method
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The idea
The substitution method solves one equation for a variable and substitutes the expression into the other, leaving one equation in one unknown.
In practice
From x + y = 7, write y = 7 − x; feed it to x − y = 3 and the y disappears: x − (7 − x) = 3.
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