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6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 1 Square Roots: The square root of a number is one of its two equal factors.

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Presentation on theme: "6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 1 Square Roots: The square root of a number is one of its two equal factors."— Presentation transcript:

1 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 1 Square Roots: The square root of a number is one of its two equal factors. (Using symbols: a is the square root of b if a 2 = b.) Example: The square root of 36 is 6 since 6 6 = 36. The square root of 36 is also – 6, since (– 6) (– 6) = 36. The positive square root is called the principle square root. We will mainly be concerned with the principle square root. The number under the radical symbol is called the radicand. (49 and 81 are the radicands.) Note: Negative real numbers do not have square roots because any nonzero real number is positive when squared. (No number multiplied by itself will give a negative real number.) Example 1. Simplify the following radical expressions. Answers: Your Turn Problem #1 Simplify the following radical expressions.

2 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 2 These examples are read: the cube root of 8 is 2 the cube root of –125 is –5 In general, x is a cube root of of y if x 3 =y. Also note, the cube root of negative number is a negative number. Example 2. Simplify the following radical expressions. Answers: Your Turn Problem #2 Simplify the following radical expressions. Answers:

3 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 3 Thus far, we have covered square roots and cube roots. There are also n th roots: 4 th roots, 5 th roots, etc. Examples: The numbers which designate the root is called the index #. The index # for the square root is a 2. However it is not usually written. Example 3. Simplify the following radical expressions. Answers: Your Turn Problem #3 Simplify the following radical expressions. Answers: Note: If the index # is even, there is no real number for the nth root of a negative number.

4 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 4 A few more examples where the radicand has an exponent equal to the index. Properties of Radicals 1 st, some examples where the radical expression is raised to a power equal to the index #. Recall that negative numbers dont have real number square roots. It is also true that negative numbers dont have real number n th roots if n is an even number. For the following properties, well assume that the radicand is positive for any even number index. Lets make some observations, then we can state another property. Writing Radical Expressions in Simplest Radical Form

5 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 5 The factors of 40 are: The largest perfect square is 4. So we will rewrite the square root using the 4 and 10. Now replace the square root of 4 with 2 and were done. Procedure: Writing Radical Expressions in Simplest Radical Form: Write the square root as a product of two square roots where one of the radicands is the largest perfect square that divides evenly into the original number. Then replace the square root with the whole number it is equal to. Leave as multiplication. Note: examples of perfect squares are 1, 4, 9, 16, 25, 36, 49, etc. The factors of 72 are: The largest perfect square is 36. So we will rewrite the square root using the 36 and 2. Now replace the square root of 36 with 6 and were done.

6 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved Write the prime factorization of 40. Another Method for Writing Square Roots in Simplest Radical Form Some students have a difficult time with the previous method. This method is a little more writing but the process is more straightforward. 1. Find the prime factorization of the given radicand. 2. Circle the pairs. 3. For every pair, one of the circled numbers will be written in front of the radical. Whatever numbers are not circled stay under the radical. (Multiply if more than one number.) 2. Circle the pairs (only a pair of 2s). 3. One 2 is written in front, the 2 and 5 remain inside. 1. Write the prime factorization of Circle the pairs (pair of 2s & 3s). 3. The 2 & 3 are written in front, the 2 remains inside. Answers: Your Turn Problem #4 Simplify the following radical expressions.

7 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 7 Rewrite the 56 with 8 and 7 since 8 is a perfect cube. Then replace the cube root of 8 with 2. Writing Cube Roots in Simplest Radical Form Method 1. Write the cube root as a product of two cube roots where one of the radicands is the largest perfect cube that divides evenly into the original number. Then replace the cube root with the integer it is equal to. Leave as multiplication. Note: examples of perfect cubes are 1, 8, 27, 64, 125, etc. Rewrite the 270 with 27 and 10 since 27 is a perfect cube. Then replace the cube root of 27 with Write the prime factorization of Circle the groups of 3 equal factors. 3. One 2 is written in front, the 7 stays inside. 1. Write the prime factorization of Circle the groups of 3 equal factors. 3. The 3 is written in front, the 2 & 5 stay inside. Method 2. Again, many students have a difficult time with method 1. This method is a little more writing but the process is more straightforward. 1. Find the prime factorization of the given radicand. 2. Circle the groups of 3 equal factors. 3. For every group of 3, one of the circled numbers will be written in front of the radical. Whatever numbers are not circled stay under the radical. (Multiply if more than one number.)

8 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 8 Your Turn Problem #5 Simplify the following radical expressions. (Write in simplest radical form.) Answers: Simplifying Square Roots that Involve Fractions We will now need the following property: In general, Property for Simplifying Radical Expressions that Involve Quotients.

9 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 9 Separate into the square root of the numerator divided by the square root of the denominator. Then simplify each (write both in simplest radical form). Separate into the square root of the numerator divided by the square root of the denominator. Then simplify each (write both in simplest radical form). Answers: Your Turn Problem #6 Simplify the following radical expressions.

10 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 10 In the last example, the denominators were perfect square roots. The numerator still contained a radical but not the denominator. A rational expression (a fraction) is not considered simplified if it contains a radical in the denominator. The process of rationalizing the denominator will take care of this. Rationalizing the Denominator (Square Roots) Observe the following: If a square root is multiplied by itself, the result is the radicand (without square root). Procedure: Rationalizing the denominator of a square root. (If the denominator contains a non-perfect square root) 2. Then simplify. Next Slide

11 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 11 Separate into the square root of the numerator divided by the square root of the denominator. Then multiply the denominator by itself and multiply the numerator by the same number. This can be simplified differently. The denominator can be written in simplest radical form 1 st before multiplying by itself. Your Turn Problem #7 Simplify the following radical expressions. Answers:

12 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 12 Rationalizing the Denominator (Cube Roots)Observe the following: A perfect cube has 3 equal factors. If a cube root is multiplied by itself, the result is not a whole number. 1. Multiply the denominator by another cube root which will make it a perfect cube root (i.e. 8, 27, 125, etc). Whatever we multiply by the denominator, we need to multiply by the numerator. Procedure: Rationalizing the denominator of a cube root. (If the denominator contains a non-perfect cube root) 2. The denominator should be a whole number. Write the numerator in simplest radical form. Reduce the fraction if possible. Next Slide

13 6.2 Roots and Radicals BobsMathClass.Com Copyright © 2010 All Rights Reserved. 13 Answer: Your Turn Problem #8 Simplify the following radical expressions. Answers: The End B.R


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