Solving equations with radicals (extraneous solutions)

In summary, when solving equations involving radicals, we must be cautious of extraneous solutions that arise when we square both sides of the equation. This is because squaring is not a reversible operation, so we may lose information about the original equation. Therefore, it is important to check our solutions to ensure they are valid.
  • #1
Mr Davis 97
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I am solving the equation ##\sqrt{x + 3} + 4 = \sqrt{8x + 1}##. I understand that , generally, to solve it, we have to eliminate the radicals by isolating a radical expression to one side and then squaring both sides of the equation.

I end up obtaining two solutions: ##x = 6## and ##x = 22/49##. Plugging these into the original equation, I find that ##x = 6## works, but ##x = 22/49## does not. I understand that the latter is termed an extraneous solution. My question is, how do these extraneous solutions arise? Does it have something to do with the fact that we lose information about the original equation when we square both sides?
 
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  • #2
Right, you lose the sign.

x = 5 has just one solution, but x2 = 25 has two. Your example is a more complex version of the same effect.
 
  • #3
Squaring both sides of an equation is not a reversible operation. Simply put, if ##a = b##, then ##a^2 = b^2##. But if you only know that ##a^2 = b^2##, then you cannot conclude that ##a = b##. Here there are two possibilities: ##a = b## and ##a = -b##. You have to be aware of what operations are reversible, and what operations are not. If all your operations are reversible, you don't have to check your solution. If some of them are not (such as squaring), then you have to check that.
 

FAQ: Solving equations with radicals (extraneous solutions)

1. What are radicals and how do they affect equations?

Radicals are mathematical expressions that involve taking the root of a number. They can affect equations by introducing additional solutions, known as extraneous solutions, which may not be valid for the original equation.

2. How do you solve equations with radicals?

To solve equations with radicals, you need to isolate the radical term on one side of the equation and then square both sides to eliminate the radical. However, it is important to check for extraneous solutions by plugging the solutions back into the original equation.

3. What is an extraneous solution?

An extraneous solution is a solution that does not satisfy the original equation. It is often introduced when solving equations with radicals because squaring both sides of an equation can introduce new solutions that are not valid for the original equation.

4. How can you avoid extraneous solutions when solving equations with radicals?

To avoid extraneous solutions, you should always check your solutions by plugging them back into the original equation. If the solution makes the equation false, then it is an extraneous solution and should be discarded.

5. Are there any tips for solving equations with radicals?

One helpful tip is to simplify the radical term as much as possible before attempting to solve the equation. This can make it easier to isolate the radical term and reduce the chances of introducing extraneous solutions. Additionally, always remember to check for extraneous solutions after solving the equation.

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