S k i l l
28 MULTIPLYING AND DIVIDING HERE IS THE RULE for multiplying radicals: It is the symmetrical version of the rule for simplifying radicals. Problem 1. Multiply. To see the answer, pass your mouse over the colored area.
Example 1. Multiply ( + )( − ). Solution. The student should recognize the form those factors will produce:
Problem 2. Multiply. a) ( + )( − ) = 5 − 3 = 2 b) (2 + )(2 − ) = 4· 3 − 6 = 12 − 6 = 6 c) (1 + )(1 − ) = 1 − (x + 1) = 1 − x − 1 = −x d) ( + )( − ) = a − b Problem 3. (x − 1 − )(x − 1 + ) a) What form does that produce? The difference of two squares. x − 1 is "a." is "b." b) Multiply out.
Problem 4. Multiply out.
Dividing radicals For example,
Problem 5. Simplify the following.
Conjugate pairs The conjugate of a + is a − . They are a conjugate pair. Example 2. Multiply 6 − with its conjugate. Solution. The product of a conjugate pair -- (6 − )(6 + ) -- is the difference of two squares. Therefore, (6 − )(6 + ) = 36 − 2 = 34 When we multiply a conjugate pair, the radical vanishes and we obtain a rational number. Problem 6. Multiply each number with its conjugate. a) x + = x² − y b) 2 − (2 − )(2 + ) = 4 − 3 = 1
d) 4 − 16 − 5 = 11 Example 3. Rationalize the denominator:
Solution. Multiply both the denominator and the numerator by the conjugate of the denominator; that is, multiply them by 3 − .
The numerator becomes 3 − . The denominator becomes the difference of the two squares.
Problem 7. Write out the steps that show the following.
Problem 9. Here is a problem that Calculus students have to do. Write out the steps that show:
In this case, you will have to rationalize the numerator.
Next Lesson: Rational exponents Please make a donation to keep TheMathPage online. Copyright © 2001-2007 Lawrence Spector Questions or comments? E-mail: themathpage@nyc.rr.com |