September 23, 2023
Learn how to identify and check extraneous solutions in equations and avoid common errors in calculations. This guide provides techniques for solving equations, identifying extraneous roots, avoiding common mistakes, and problem-solving examples using quadratic equations and more.


Equations are fundamental tools in mathematics, and it is essential to check the validity of the solutions obtained from them. However, sometimes equations produce additional solutions that do not satisfy the original equation. These are called extraneous solutions or roots. In this article, we will explore what extraneous solutions are, why they occur, and most importantly, how to identify and check them. This guide is designed for anyone studying equations, from students to professionals.

What are Extraneous Solutions?

An extraneous solution is a solution to an equation that does not satisfy the original equation or problem. They appear when simplifying or solving complex equations. In simpler terms, the solution is “extraneous” or irrelevant to the original problem. Extraneous solutions can cause errors in calculations or misinterpretations of the problem, leading to wrong answers.

For example, consider the equation: √(x+3) = x-1. The correct solution to this equation is x=4, obtained by squaring both sides of the equation. However, when we substitute x=4 back into the original equation, we get √7 on the left-hand side, which is not equivalent to 4-1=3 on the right-hand side. This is an extraneous solution.

Extraneous solutions occur in more complex equations involving fractional exponents, radicals, denominators, or squared or cubed terms.

Guide on How to Check for Extraneous Solutions

Here are some steps and techniques to help identify and check extraneous solutions:

  • Step 1: Solve the equation as usual and get the value of the variable.
  • Step 2: Substitute the value of the variable obtained in step 1 back into the original equation.
  • Step 3: Simplify both sides of the equation obtained in step 2 as much as possible.
  • Step 4: Compare the simplification on both sides of the equation. If the two sides are not equal, it means that the solution obtained is extraneous.

Another technique to check for extraneous solutions is to graph the equation and examine the intersection of the graph with any asymptotes or limits. Extraneous solutions appear as points that lie outside the domain of the original problem or equation.

Common Types of Equations that Produce Extraneous Solutions

Here are some common types of equations that produce extraneous solutions:

  • Equations involving radicals and fractional exponents.
  • Equations that involve the squaring of both sides of the equation.
  • Equations involving a radical that has a variable or expression in the denominator.
  • Equations involving the division of polynomials.
  • Equations that have domain definitions, asymptotes, or limits.

It is important to be aware of these common types of equations that may produce extraneous roots, so you can check for them and avoid errors in calculations.

Problem Solving Techniques for Avoiding Extraneous Solutions

Here are some problem-solving techniques that can help you avoid extraneous roots in your solutions:

  • Keep track of the domain of the solutions and avoid using values that fall outside of it.
  • Reduce and simplify the equation before attempting to solve it.
  • Avoid squaring both sides of the equation unless it is necessary.
  • Use substitution techniques to simplify equations and avoid extraneous roots.

Common Mistakes that Lead to Extraneous Solutions

Here are some common mistakes that lead to extraneous solutions:

  • Ignoring the domain of the solution.
  • Not keeping track of negative signs or imaginary numbers.
  • Using assumptions to simplify the equation.
  • Relying too much on memorization, instead of understanding the steps to solve the equation.
  • Skipping steps during the problem-solving process.

To avoid these mistakes, it is crucial to take your time in solving equations and double-checking your work.

Examples of Equations with Extraneous Solutions and How to Solve Them

Here are some examples of equations with extraneous solutions:

Example 1:

Solve for x: √(2x+6) = x+3

Squaring both sides of the equation, we get: 2x+6 = (x+3)². Expanding, we get: 2x+6 = x²+6x+9. Moving all terms to one side, we get: x²+4x+3=0. By factoring, we get: (x+1)(x+3)=0. Thus, x=-1, -3.

When we substitute x=-1 into the original equation, we get 0=-2, which is not valid. Therefore, x=-1 is an extraneous solution.

The correct answer is x=-3.

Example 2:

Solve for x: (x-3)/(x-5) + 1/(x-5) = (x+1)/(x-5)

We have a fraction equation, so we need to find a common denominator on both sides: ((x-3)+1)/(x-5) = (x+1)/(x-5). Simplifying, we get (x-2)/(x-5) = (x+1)/(x-5). Cross-multiplying, we get: (x-2)(x-5) = (x+1)(x-5). Simplifying, we get: x²-5x-10=0. Solving by quadratic formula, we get: x = (5+√65)/2, (5-√65)/2.

Both these solutions are valid because they fall within the domain of the equation.


Extraneous solutions can be a common pitfall when solving equations, leading to wrong answers or errors. To avoid this, it is essential to understand what extraneous solutions are, how to check for them, and the problem-solving techniques to use to avoid them. In this guide, we have explored all these and provided tips on solving equations using examples. It is now up to the reader to apply this knowledge in their equations and avoid making mistakes.

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