Algebra · Simultaneous equations
Chapter 1 · 3
The idea
Substitution and real-world simultaneous equations
Why substitution collapses two equations into one, the bracket that guards every substitution, and how to translate two-fact word problems (prices, sums, perimeters, intersections) into a solvable pair.
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Algebra · Simultaneous equations
Substitution and real-world simultaneous equations
Why substitution collapses two equations into one, the bracket that guards every substitution, and how to translate two-fact word problems (prices, sums, perimeters, intersections) into a solvable pair.
Why it works
Trade one unknown for the other
Substitution trades one unknown for the other. If one equation already isolates a variable — — then wherever the other equation says , you may write instead:Two equations became one equation in one unknown — the familiar kind. Substitution shines exactly when a formula-form equation () is already on the table; elimination shines when both equations are in shape.
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The rest of the explanation, plus 2 worked examples you step through move by move.
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