Substitution Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

medium
If y=x+3y = x + 3 and 2x+y=92x + y = 9, use substitution to solve for xx.

Solution

  1. 1
    Replace yy in the second equation with (x+3)(x + 3): 2x+(x+3)=92x + (x + 3) = 9.
  2. 2
    Simplify: 3x+3=93x + 3 = 9.
  3. 3
    Subtract 3: 3x=63x = 6, so x=2x = 2.

Answer

x=2x = 2
Substitution can replace a variable with an equivalent expression (not just a number). This is the basis of the substitution method for solving systems of equations.

About Substitution

Replacing every occurrence of a variable or sub-expression with an equivalent value or expression throughout a problem.

Learn more about Substitution →

More Substitution Examples

Example 1 easy

If [formula] and [formula], find [formula].

Example 3 easy

Evaluate [formula] when [formula] and [formula].

Example 4 medium

If [formula] and [formula], find [formula].

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