Tài liệu Master the Gre 2010 - Part 26 pdf

MULTIPLICATION AND DIVISION

Terms under different radicals can be combined under a common radical if one term is

multiplied or divided by the other. But if the radicals are different (for example, square

root and cube root), combining terms is a bit tricky—as in the last example below.

=x=x 5~=x!

2

or x

=x=y 5 =xy

=x

=y

5 Îx

y

=3

x=x 5 x

1/3

x

1/2 5 x

1/3 1 1/2 5 x

5/6

14. ~2=2a!

2 5

(A) 4a

(B) 4a2

(C) 8a

(D) 8a2

(E) 6a

The correct answer is (C). Square each of the two terms, 2 and =2a, sepa￾rately. Then combine their squares by multiplication: ~2=2a!

2 5 22 3 ~=2a!

2 5

4 3 2a 5 8a.

Roots You Should Know

For the GRE, memorize the roots in the following table. If you encounter one of these

radical terms on the exam, chances are you’ll need to know its equivalent integer to

answer the question.

In the table, notice that the cube root of a negative number is negative and the cube

root of a positive number is positive.

Chapter 10: Math Review: Number Theory and Algebra 233

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