Solve A System Of Equations - Using Substitution

🔑 Key Concepts

  • Use substitution when one equation already has a variable isolated or can be rewritten easily.
  • Replace the isolated variable in the other equation with its equivalent expression.
  • Substitution creates an equation containing only one variable.
  • After finding one variable, substitute its value back into either original equation.
  • Write the solution as an ordered pair \((x,y)\).
  • The ordered pair represents the point where the two lines intersect.
  • Check the solution in both original equations.

✏️ Worked Examples — Solving Systems by Substitution

🧠 Math Vocabulary

  • System of equations: Two or more equations containing the same variables.
  • Substitution: Replacing a variable with an equivalent value or expression.
  • Solution of a system: The ordered pair that makes both equations true.
  • Ordered pair: A solution written as \((x,y)\).
  • Intersection: The point where the graphs of two equations meet.
  • Isolate: Rewrite an equation so one variable is alone on one side.

💡 Main Idea

To solve a system using substitution, isolate one variable and replace that variable in the other equation with its equivalent expression. Solve the resulting one-variable equation, substitute back to find the second variable, and write the solution as the ordered pair where the two lines intersect.

📚 What You Should Already Know

Students should know how to solve multi-step equations, distribute multiplication, combine like terms, perform integer operations, isolate variables, and substitute values or expressions into equations.

🚀 What Comes Next

Students will compare substitution with elimination and graphing, identify systems with no solution or infinitely many solutions, and apply systems of equations to real-world situations.

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