Roots and Radicals

# 75 Multiply Square Roots

### Learning Objectives

By the end of this section, you will be able to:

- Multiply square roots
- Use polynomial multiplication to multiply square roots

Before you get started, take this readiness quiz.

### Multiply Square Roots

We have used the Product Property of Square Roots to simplify square roots by removing the perfect square factors. The Product Property of Square Roots says

We can use the Product Property of Square Roots ‘in reverse’ to multiply square roots.

Remember, we assume all variables are greater than or equal to zero.

We will rewrite the Product Property of Square Roots so we see both ways together.

If *a*, *b* are nonnegative real numbers, then

So we can multiply in this way:

Sometimes the product gives us a perfect square:

Even when the product is not a perfect square, we must look for perfect-square factors and simplify the radical whenever possible.

Multiplying radicals with coefficients is much like multiplying variables with coefficients. To multiply we multiply the coefficients together and then the variables. The result is . Keep this in mind as you do these examples.

Simplify: ⓐ ⓑ .

- ⓐ
- ⓑ

Notice that in (b) we multiplied the coefficients and multiplied the radicals. Also, we did not simplify . We waited to get the product and then simplified.

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: .

Simplify: .

Simplify: .

When we have to multiply square roots, we first find the product and then remove any perfect square factors.

Simplify: ⓐ ⓑ .

- ⓐ
- ⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: .

Simplify: .

Simplify: .

Simplify: ⓐ ⓑ .

ⓐ

ⓑ

Simplify: ⓐ ⓑ .

ⓐ 12 ⓑ

Simplify: ⓐ ⓑ .

ⓐ 16 ⓑ 20

The results of the previous example lead us to this property.

If *a* is a nonnegative real number, then

By realizing that squaring and taking a square root are ‘opposite’ operations, we can simplify and get 2 right away. When we multiply the two like square roots in part (a) of the next example, it is the same as squaring.

Simplify: ⓐ ⓑ .

ⓐ

ⓑ

Simplify: ⓐ ⓑ .

ⓐ 330 ⓑ 200

Simplify: ⓐ ⓑ .

ⓐ 210 ⓑ 96

### Use Polynomial Multiplication to Multiply Square Roots

In the next few examples, we will use the Distributive Property to multiply expressions with square roots.

We will first distribute and then simplify the square roots when possible.

Simplify: ⓐ ⓑ .

ⓐ

ⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐ

ⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

When we worked with polynomials, we multiplied binomials by binomials. Remember, this gave us four products before we combined any like terms. To be sure to get all four products, we organized our work—usually by the FOIL method.

Simplify: .

Simplify: .

Simplify: .

Simplify: .

Simplify: .

Simplify: .

Simplify: .

Simplify: .

Simplify:

Simplify: .

Simplify: .

Simplify: .

Note that some special products made our work easier when we multiplied binomials earlier. This is true when we multiply square roots, too. The special product formulas we used are shown below.

We will use the special product formulas in the next few examples. We will start with the Binomial Squares formula.

Simplify: ⓐ ⓑ .

Be sure to include the term when squaring a binomial.

- ⓐ

Multiply using the binomial square pattern. Simplify. Combine like terms. - ⓑ

Multiply using the binomial square pattern. Simplify. Combine like terms.

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: ⓐ ⓑ .

ⓐⓑ

Simplify: .

Multiply using the binomial square pattern. | |

Simplify. |

Simplify: .

Simplify: .

In the next two examples, we will find the product of conjugates.

Simplify: .

Multiply using the binomial square pattern. | |

Simplify. |

Simplify: .

Simplify: .

Simplify: .

Multiply using the binomial square pattern. | |

Simplify. |

Simplify: .

Simplify: .

Access these online resources for additional instruction and practice with multiplying square roots.

### Key Concepts

**Product Property of Square Roots**If*a*,*b*are nonnegative real numbers, then

**Special formulas**for multiplying binomials and conjugates:

- The FOIL method can be used to multiply binomials containing radicals.

#### Practice Makes Perfect

**Multiply Square Roots**

In the following exercises, simplify.

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ 160

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐ 11 ⓑ 21

ⓐ

ⓑ

ⓐ

ⓑ

ⓐ 23 ⓑ 3

ⓐ

ⓑ

ⓐ

ⓑ

ⓐ −234 ⓑ 180

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ 56

**Use Polynomial Multiplication to Multiply Square Roots**

In the following exercises, simplify.

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

ⓐ

ⓑ

ⓐ

ⓑ

ⓐⓑ

97

39

33

**Mixed Practice**

In the following exercises, simplify.

#### Everyday Math

A landscaper wants to put a square reflecting pool next to a triangular deck, as shown below. The triangular deck is a right triangle, with legs of length 9 feet and 11 feet, and the pool will be adjacent to the hypotenuse.

- ⓐ Use the Pythagorean Theorem to find the length of a side of the pool. Round your answer to the nearest tenth of a foot.
- ⓑ Find the exact area of the pool.

An artist wants to make a small monument in the shape of a square base topped by a right triangle, as shown below. The square base will be adjacent to one leg of the triangle. The other leg of the triangle will measure 2 feet and the hypotenuse will be 5 feet.

- ⓐ Use the Pythagorean Theorem to find the length of a side of the square base. Round your answer to the nearest tenth of a foot.

- ⓑ Find the exact area of the face of the square base.

ⓐⓑ

A square garden will be made with a stone border on one edge. If only feet of stone are available, simplify to determine the area of the largest such garden.

A garden will be made so as to contain two square sections, one section with side length yards and one section with side length yards. Simplify to determine the total area of the garden.

Suppose a third section will be added to the garden in the previous exercise. The third section is to have a width of feet. Write an expression that gives the total area of the garden.

#### Writing Exercises

- ⓐ Explain why is always positive, for .
- ⓑ Explain why is always negative, for .

ⓐ when squaring a negative, it becomes a positive ⓑ since the negative is not included in the parenthesis, it is not squared, and remains negative

Use the binomial square pattern to simplify . Explain all your steps.

#### Self Check

ⓐ After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

ⓑ On a scale of 1–10, how would you rate your mastery of this section in light of your responses on the checklist? How can you improve this?