Mathematics - Algebra - Systems of Equations - Solving systems by substitution - The Replacement Trick

'If y=x+3, and 2x+y=15, we know y equals x+3. So we can REPLACE y in the second equation!' 2x+(x+3)=15 → 3x+3=15 → x=4 → y=7. Do 3 quick problems where one variable is already isolated. Students see substitution as 'replacing one variable with what it equals.'

Edodovivmagarwal
Mathematics - Algebra - Systems of Equations - Solving systems by substitution - The Replacement Trick
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Mathematics - Algebra - Systems of Equations - Solving systems by substitution - The Replacement Trick

vivmagarwal
vivmagarwalJan 29, 2026

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'If y=x+3, and 2x+y=15, we know y equals x+3. So we can REPLACE y in the second equation!' 2x+(x+3)=15 → 3x+3=15 → x=4 → y=7. Do 3 quick problems where one variable is already isolated. Students see substitution as 'replacing one variable with what it equals.'

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MathematicsAlgebra - Systems of EquationsStage 9, Grade 8, Class 10, MYP Grade 9, Class 10

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