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MATH 1150 · Radical expressions · Objective 1.4

Rationalize Monomial Denominators

Remove a radical from a one-term denominator using a form of 1.

CLO 1 · Topic 18 of 21
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Build the concept from the beginning

Meaning before procedure

Rationalizing multiplies numerator and denominator by a factor that makes the denominator a perfect power. For 1/√a, multiply by √a/√a to obtain √a/a.

Rational denominator
A denominator containing no radical.
Form of 1
An equal numerator and denominator that preserves value.
Completing a power
Supplying missing factors needed for a perfect nth power.
Restriction
The original denominator cannot equal zero.

Interactive visual model

Build the missing factor that turns a radical denominator into a perfect power.

Change one control at a time and describe what changes—and what stays invariant.

A dependable four-step method

Inspect the denominator and index.
Choose the factor that completes a perfect power.
Multiply numerator and denominator.
Simplify and preserve original restrictions.
  1. Inspect the denominator and index.
  2. Choose the factor that completes a perfect power.
  3. Multiply numerator and denominator.
  4. Simplify and preserve original restrictions.
Three fully explained examples

Watch the reasoning, not just the answer

Example 1: Rationalize 1/√5.

Name the goalThe denominator needs another √5 factor.
Choose the next moveMultiply by √5/√5.
Carry out the mathematics√5/(√5·√5) = √5/5.
Check and interpretThe new fraction is equivalent and has rational denominator 5.

Example 2: Rationalize 3/(2√7).

Name the goalOnly √7 needs a matching factor.
Choose the next moveMultiply by √7/√7.
Carry out the mathematics3√7/(2·7) = 3√7/14.
Check and interpretNo common factor remains.

Example 3: Rationalize 1/∛4.

Name the goalMake the radicand a perfect cube.
Choose the next move4 = 2² needs one more factor 2, so multiply by ∛2/∛2.
Carry out the mathematics∛2/∛8 = ∛2/2.
Check and interpretThe denominator is now rational.
Interactive practice

Predict, decide, check, and revise

Interactive construction lab

Build a valid reasoning path

Choose the decisions in the order a careful solver would use them for this concept.

Choose this step, then check the construction.
Choose this step, then check the construction.
Choose this step, then check the construction.

The reasoning path changes as each decision is selected.

Readiness check

Check the foundation

Rationalize 1/√2.

Rationalize 1/√3.

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Guided practice

Apply the method with support

Rationalize 1/√5.

Rationalize 2/√7.

Rationalize 3/√2.

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Independent practice

Work without step prompts

Rationalize 5/(2√3).

Rationalize 7/(3√5).

Rationalize 4/√11.

Rationalize 1/∛2.

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Mastery check

Demonstrate durable understanding

Rationalize 1/∛4.

Rationalize 2/∛3.

Rationalize 3/∛9.

Rationalize 1/⁴√2.

Rationalize 1/⁴√8.

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Unfamiliar transfer

Explain, compare, and revise

Rationalize 5/∛(9x), assuming x ≠ 0 and the real expression is defined.

Write a first attempt before opening the self-check.

The learner record reveals exact answers and model reasoning only after an attempt.