# Multiplying, Dividing, and Simplifying Radicals

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8.2 Multiplying, Dividing, and Simplifying Radicals 1 Multiply square root radicals. Simplify radicals by using the product rule. Simplify radicals by using the quotient rule. Simplify radicals involving variables. Simplify other roots. 2 3 4 5

Product Rule for Radicals For nonnegative real numbers a and b, and That is, the product of two square roots is the square root of the product, and the square root of a product is the product of the square roots. It is important to note that the radicands not be negative numbers in the product rule. Also, in general,

EXAMPLE 1 Using the Product Rule to Multiply Radicals Find each product. Assume that Solution:

Simplify radicals by using the product rule.
A square root radical is simplified when no perfect square factor remains under the radical sign. This can be accomplished by using the product rule:

EXAMPLE 2 Using the Product Rule to Simplify Radicals Simplify each radical. Solution:

EXAMPLE 3 Multiplying and Simplifying Radicals Find each product and simplify. Solution:

Simplify radicals by using the quotient rule.
The quotient rule for radicals is similar to the product rule.

EXAMPLE 4 Using the Quotient Rule to Simplify Radicals Simplify each radical. Solution:

EXAMPLE 5 Using the Quotient Rule to Divide Radicals Simplify. Solution:

EXAMPLE 6 Using Both the Product and Quotient Rules Simplify. Solution:

Radicals can also involve variables. The square root of a squared number is always nonnegative. The absolute value is used to express this. The product and quotient rules apply when variables appear under the radical sign, as long as the variables represent only nonnegative real numbers

EXAMPLE 7 Simplifying Radicals Involving Variables Simplify each radical. Assume that all variables represent positive real numbers. Solution:

Find cube, fourth, and other roots.
Finding the square root of a number is the inverse of squaring a number. In a similar way, there are inverses to finding the cube of a number or to finding the fourth or greater power of a number. The nth root of a is written In the number n is the index or order of the radical. Radical sign Index Radicand It can be helpful to complete and keep a list to refer to of third and fourth powers from 1-10.

Simplify other roots. To simplify cube roots, look for factors that are perfect cubes. A perfect cube is a number with a rational cube root. For example, , and because 4 is a rational number, 64 is a perfect cube. Properties of Radicals For all real number for which the indicated roots exist,

EXAMPLE 9 Finding Cube Roots Solution: Find each cube root.

EXAMPLE 8 Simplifying Other Roots Simplify each radical. Solution:

EXAMPLE 10 Finding Other Roots Find each root. Solution:

EXAMPLE 9 Simplifying Cube Roots Involving Variables Simplify each radical. Solution:

We add or subtract radicals by using the distributive property. For example, Radicands are different Indexes are different Only like radicals — those which are multiples of the same root of the same number — can be combined this way. The preceding example shows like radicals. By contrast, examples of unlike radicals are Note that cannot be simplified.

Sometimes, one or more radical expressions in a sum or difference must be simplified. Then, any like radicals that result can be added or subtracted.

When simplifying more complicated radical expressions, recall the rules for order of operations. A sum or difference of radicals can be simplified only if the radicals are like radicals. Thus, cannot be simplified further.

EXAMPLE 3 Simplifying Radical Expressions Simplify each radical expression. Assume that all variables represent nonnegative real numbers. Solution:

EXAMPLE 3 Simplifying Radical Expressions (cont’d) Simplify each radical expression. Assume that all variables represent nonnegative real numbers. Solution:

Rationalizing the Denominator
8.4 Rationalizing the Denominator 1 Rationalize denominators with square roots. Write radicals in simplified form. Rationalize denominators with cube roots. 2 3

Rationalize denominators with square roots.
It is easier to work with a radical expression if the denominators do not contain any radicals. This process of changing the denominator from a radical, or irrational number, to a rational number is called rationalizing the denominator. The value of the radical expression is not changed; only the form is changed, because the expression has been multiplied by 1 in the form of

EXAMPLE 1 Rationalizing Denominators Rationalize each denominator. Solution:

Conditions for Simplified Form of a Radical 1. The radicand contains no factor (except 1) that is a perfect square (in dealing with square roots), a perfect cube (in dealing with cube roots), and so on. 2. The radicand has no fractions. 3. No denominator contains a radical.

EXAMPLE 2 Simplifying a Radical Simplify Solution:

EXAMPLE 3 Simplifying a Product of Radicals Simplify Solution:

EXAMPLE 4 Simplifying Quotients Involving Radicals Simplify. Assume that p and q are positive numbers. Solution:

EXAMPLE 5 Rationalizing Denominators with Cube Roots Rationalize each denominator. Solution:

More Simplifying and Operations with Radicals
8.5 More Simplifying and Operations with Radicals 1 Simplify products of radical expressions. Use conjugates to rationalize denominators of radical expressions. Write radical expressions with quotients in lowest terms. 2 3

EXAMPLE 1 Multiplying Radical Expressions Find each product and simplify. Solution:

EXAMPLE 1 Multiplying Radical Expressions (cont’d) Find each product and simplify. Solution:

EXAMPLE 2 Using Special Products with Radicals Find each product. Assume that x ≥ 0. Solution: Remember only like radicals can be combined!

Using a Special Product with Radicals.
Example 3 uses the rule for the product of the sum and difference of two terms,

EXAMPLE 3 Using a Special Product with Radicals Find each product. Assume that Solution:

Use conjugates to rationalize denominators of radical expressions.
The results in the previous example do not contain radicals. The pairs being multiplied are called conjugates of each other. Conjugates can be used to rationalize the denominators in more complicated quotients, such as Using Conjugates to Rationalize a Binomial Denominator To rationalize a binomial denominator, where at least one of those terms is a square root radical, multiply numerator and denominator by the conjugate of the denominator.

EXAMPLE 4 Using Conjugates to Rationalize Denominators Simplify by rationalizing each denominator. Assume that Solution:

EXAMPLE 4 Using Conjugates to Rationalize Denominators (cont’d) Simplify by rationalizing each denominator. Assume that Solution:

EXAMPLE 5 Writing a Radical Quotient in Lowest Terms Write in lowest terms. Solution:

Using Rational Numbers as Exponents
8.7 Using Rational Numbers as Exponents 1 Define and use expressions of the form a1/n. Define and use expressions of the form am/n. Apply the rules for exponents using rational exponents. Use rational exponents to simplify radicals. 2 3 4

Define and use expressions of the form a1/n.
Now consider how an expression such as 51/2 should be defined, so that all the rules for exponents developed earlier still apply. We define 51/2 so that 51/2 · 51/2 = 51/2 + 1/2 = 51 = 5. This agrees with the product rule for exponents from Section 5.1. By definition, Since both 51/2 · 51/2 and equal 5, this would seem to suggest that 51/2 should equal Similarly, then 51/3 should equal Review the basic rules for exponents: Slide 8.7-4

a1/n Define and use expressions of the form a1/n.
If a is a nonnegative number and n is a positive integer, then Notice that the denominator of the rational exponent is the index of the radical. Slide 8.7-5

491/2 10001/3 811/4 EXAMPLE 1 Using the Definition of a1/n Simplify.
Solution: Slide 8.7-6

Define and use expressions of the form am/n.
Now we can define a more general exponential expression, such as 163/4. By the power rule, (am)n = amn, so However, 163/4 can also be written as Either way, the answer is the same. Taking the root first involves smaller numbers and is often easier. This example suggests the following definition for a m/n. am/n If a is a nonnegative number and m and n are integers with n > 0, then Slide 8.7-8

95/2 85/3 –272/3 EXAMPLE 2 Using the Definition of am/n Evaluate.
Solution: Slide 8.7-9

Using the definition of am/n.
Earlier, a–n was defined as for nonzero numbers a and integers n. This same result applies to negative rational exponents. a−m/n If a is a positive number and m and n are integers, with n > 0, then A common mistake is to write 27–4/3 as –273/4. This is incorrect. The negative exponent does not indicate a negative number. Also, the negative exponent indicates to use the reciprocal of the base, not the reciprocal of the exponent. Slide

36–3/2 81–3/4 EXAMPLE 3 Using the Definition of a−m/n Evaluate.
Solution: Slide

Apply the rules for exponents using rational exponents.
All the rules for exponents given earlier still hold when the exponents are fractions. Slide

EXAMPLE 4 Using the Rules for Exponents with Fractional Exponents Simplify. Write each answer in exponential form with only positive exponents. Solution: Slide

Using Fractional Exponents with Variables
EXAMPLE 5 Using Fractional Exponents with Variables Simplify. Write each answer in exponential form with only positive exponents. Assume that all variables represent positive numbers. Solution: Slide

Use rational exponents to simplify radicals.
Sometimes it is easier to simplify a radical by first writing it in exponential form. Slide

Simplifying Radicals by Using Rational Exponents
EXAMPLE 6 Simplifying Radicals by Using Rational Exponents Simplify each radical by first writing it in exponential form. Solution: Slide

8.6 Solving Equations with Radicals 1 Solve radical equations having square root radicals. Identify equations with no solutions. Solve equations by squaring a binomial. Solve radical equations having cube root radicals. 2 3 4

A radical equation is an equation having a variable in the radicand, such as or

To solve radical equations having square root radicals, we need a new property, called the squaring property of equality. Squaring Property of Equality If each side of a given equation is squared, then all solutions of the original equation are among the solutions of the squared equation. Be very careful with the squaring property: Using this property can give a new equation with more solutions than the original equation has. Because of this possibility, checking is an essential part of the process. All proposed solutions from the squared equation must be checked in the original equation.

Using the Squaring Property of Equality
EXAMPLE 1 Using the Squaring Property of Equality Solve. Solution: It is important to note that even though the algebraic work may be done perfectly, the answer produced may not make the original equation true.

EXAMPLE 2 Solve. Solution:
Using the Squaring Property with a Radical on Each Side Solve. Solution:

EXAMPLE 3 Solve. Solution: Check: False
Using the Squaring Property When One Side Is Negative Solve. Solution: Check: False Because represents the principal or nonnegative square root of x in Example 3, we might have seen immediately that there is no solution.

Step 1 Isolate a radical. Arrange the terms so that a radical is isolated on one side of the equation. Step 2 Square both sides. Step 3 Combine like terms. Step 4 Repeat Steps 1-3 if there is still a term with a radical. Step 5 Solve the equation. Find all proposed solutions. Step 6 Check all proposed solutions in the original equation.

Solve EXAMPLE 4 Solution:
Using the Squaring Property with a Quadratic Expression Solve Solution: Since x must be a positive number the solution set is Ø.

or EXAMPLE 5 Solve Solution:
Using the Squaring Property when One Side Has Two Terms Solve Solution: or Since 2x-1 must be positive the solution set is {4}.

or EXAMPLE 6 Solve. Solution: The solution set is {4,9}.
Rewriting an Equation before Using the Squaring Property Solve. Solution: or The solution set is {4,9}.

Solve equations by squaring a binomial.
Errors often occur when both sides of an equation are squared. For instance, when both sides of are squared, the entire binomial 2x + 1 must be squared to get 4x2 + 4x + 1. It is incorrect to square the 2x and the 1 separately to get 4x2 + 1.

EXAMPLE 7 Using the Squaring Property Twice Solve. Solution: The solution set is {8}.