How to Solve Irrational Functions?

Irrational functions are generally considered to be functions that have a radical sign. In this post, you will learn more about the definition of irrational functions.

How to Solve Irrational Functions?
Tutor-style math help

Solve Irrational Functions: what to notice and how to work it

Radicals skill
Radicals are roots. Simplifying or solving with radicals is mostly about perfect powers, domain restrictions, and checking for extraneous answers.

What to notice first

Look for perfect-square, perfect-cube, or matching index factors before reaching for a calculator.

Common student mistake

Do not split a radical across addition. \(\sqrt{a+b}\) is not usually \(\sqrt a+\sqrt b\).

Key formulas and cues

\(\sqrt{ab}=\sqrt a\sqrt b\)
\(x^{m/n}=\sqrt[n]{x^m}\)
\(\sqrt{x}\text{ requires }x\ge0\)
\(\text{squaring can create extraneous answers}\)

A reliable path

  1. Find perfect powersBreak the radicand into a perfect power times a leftover factor.
  2. Watch the domainEven roots need nonnegative radicands in real-number problems.
  3. Check solutionsIf you squared both sides, test answers in the original equation.

Worked examples

Simplify a radical

Example: \(\sqrt{72}\)
  1. 72 = 36 times 2.
  2. The square root of 36 is 6.
  3. Leave the leftover 2 inside.
Answer: \(6\sqrt2\)

Find a radical domain

Example: \(y=\sqrt{x-4}\)
  1. The radicand is x – 4.
  2. Require x – 4 >= 0.
  3. Solve the inequality.
Answer: \(x\ge4\)
Try one before moving on
Try: Simplify \(\sqrt{98}\).
Answer: \(7\sqrt2\).
Next step: do the matching worksheet or quiz while the method is still fresh, then come back and explain the first step in your own words.

Related Topics

A step-by-step guide to irrational functions

An irrational function can be said to be a function that cannot be written as the quotient of two polynomials, but this definition is not usually used. In general, the most commonly used definition is that an irrational function is a function that contains variables in the radicals, i.e., square roots, cube roots, etc.

Therefore, the fundamental form of an irrational function is:

\(\color{blue}{f\left(x\right)=\sqrt[n]{\left(g\left(x\right)\right)^m}}\) or \(\color{blue}{f\left(x\right)=\left(g\left(x\right)\right)^{\left(\frac{m}{n}\right)}}\)

Where \(g(x)\) is a rational function.

  • If the index \(n\) of the radical is odd, it is possible to calculate the domain of all real numbers.
  • If the index \(n\) of the radical is even, we need \(g(x)\) to be positive or zero since the even roots of a negative number are not real.

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