Understanding the Algebraic Principle: Subtract 15 from Both Sides of an Equation

In algebra, solving equations often involves simplifying expressions to isolate the variable. One powerful and fundamental technique is subtracting 15 from both sides of an equation. This approach maintains equality and helps solve for unknown values efficiently. In this article, we explore how subtracting 15 from both sides works, why it’s effective, and some common applications.

Understanding the Context

What Does “Subtract 15 from Both Sides” Mean?

When solving an equation, the key principle is that whatever operation you perform on one side, you must do to the other side to preserve equality. Subtracting 15 from both sides means performing the same operation equally on both expressions. For example:

If you have
x – 15 = 28,
you subtract 15 from both sides:
x – 15 – 15 = 28 – 15,
which simplifies to
x – 30 = 13.

Now, you can easily solve for x by adding 30 to both sides.

Subtract 15 from both sides:

Key Insights

Why Subtract 15 from Both Sides?

The goal is to simplify expressions and eliminate constants that block progress toward solving for a variable. Subtracting 15 helps:

  • Isolate variables: Removing a constant adjacent to the variable makes it possible to solve.
  • Maintain balance: By applying the same subtraction on both sides, the equation remains valid.
  • Streamline complex equations: Multiple such operations help unravel multi-step or layered problems.

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Final Thoughts

Real-Life Application Example

Let’s solve this step-by-step:

Problem:
Solve for x:
x – 15 = 22

Solution:

  1. Original equation:
    x – 15 = 22

  2. Subtract 15 from both sides:
    x – 15 – 15 = 22 – 15
    x – 30 = 7

  3. Add 30 to both sides:
    x = 7 + 30
    x = 37

Jack’s equation shows how subtracting 15 unblocks the value of x.

When Is This Technique Useful?

  • Solving linear equations with constants
  • Verifying equality in expressions
  • Simple algebraic proofs where constants must be eliminated
  • Education purposes for teaching balance and equivalence in equations