Lesson 3 MA 15200 - Purdue University



Lesson 3 MA 15200

Definition of a root: If n is a natural number greater than 1 and [pic], then [pic] is the nonnegative number whose nth power is a. [pic]

In the radical expression [pic] , the symbol [pic] is called the radical sign, a is the radicand, and n is the index. (If the index is 2, a square root, usually the index is not written. If the index is 3, the expression is called a cube root. Otherwise, it is an nth root.)

If n is a natural number greater than 1 and [pic], then [pic] is the nonnegative number whose nth power is a. [pic] If [pic], sometimes [pic] is defined, sometimes not.

If [pic]is the non-negative number whose nth power is a. [pic]

If a < 0, and [pic]

If a is a negative, then [pic] would not be real. If a is positive or zero, then [pic] would be real. To avoid confusion, we will always assume that a variable represents a positive value.

Ex 1: Evaluate each.

[pic]

Multiplication and Division Properties of Radicals:

Examine: [pic]

If all expressions represent real numbers,

[pic]

Note: These properties are for multiplication and division. Similar statements are not true for addition or subtraction. ([pic], for example)

Numbers that are squares of positive integers; such as 1, 4, 9, 16, ...; are called perfect squares. Powers such as [pic], ... are also called perfect squares.

Numbers that are cubes of positive integers; such as 1, 8, 27, 64,....; are called perfect cubes. Powers such as [pic] are also called perfect cubes.

To simplify a radical expression:

1. Factor the radicand into the greatest perfect factor possible and a 'leftover' factor.

2. Use the multiplication property of radicals to 'separate' into two radicals.

3. Simplify the 'perfect factor' radical.

Ex 2: Simplify each.

[pic]

Racial expressions with the same index and the same radicand are called like radicals. Like radicals can be combined similar to like terms. *When trying to combine radicals, always simplify radicals first!

Ex 3: Simplify and combine where possible.

[pic]

Rationalizing Denominators: Rationalizing a denominator translates ‘write the expression without a radical in the denominator’. To rationalize when there is a square root in the denominator, do the following steps.

1. First, simplify each radical.

2. Multiply numerator and denominator by the radical factor in the denominator.

3. Simplify numerator and denominator.

Ex 4: Rationalize the denominator.

[pic]

Definition of a Rational Exponent (1):

If [pic]then [pic]is the real number b such that [pic], if b exists. Basically,[pic].

Ex 5: Evaluate each.

[pic]

Ex 6: Evaluate each.

[pic]

Other Rational Exponents (2):

Definition: If m and n are positive integers, the fraction [pic] is in lowest terms, and [pic] exists, then [pic].

This definition shows that [pic]can be evaluated two different ways;

(1) take the nth root first, then raise to the mth power or

(2) raise to the mth power first, then take the nth root.

It is usually to the student's advantage to take the root first, then ‘raise to the power’.

Ex 7: Evaluate each.

[pic]

All the rules of exponents previously studied now apply also with rational exponents.

Ex 8: Assume that all variables represent positive integers. Evaluate or simplify each and write all answers without using negative exponents.

[pic]

Ex 9: Simplify each using the rules of exponents. Assume that all variables represent positive integers. Write answers without using negative exponents.

[pic]

[pic]

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