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Practice Exam 1 - GMAT Prep - Algebra

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lucas211: Senior | Next Rank: 100 Posts; Posts: 97; Joined: Mon Aug 04, 2014 5:39 pmFollowed by: 2 members; Thanked: 1 times

by lucas211 » Wed May 25, 2016 4:22 pm

Hello BTG

Would appreciate some help on the following question.

Thanks

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Source: Beat The GMAT — Problem Solving | Wed May 25, 2016 4:22 pm

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed May 25, 2016 4:27 pm

if xy=1 then what is the value of 2^(x+y)Â²/ 2^(x-y)Â²

1)2
2) 4
3) 8
4) 16
5) 32

2^(x+y)Â²/ 2^(x-y)Â² = 2^(xÂ² + 2xy + yÂ²)/ 2^(xÂ² - 2xy + yÂ²)
= 2^(4xy) [after we subtract exponents]
= 2^4 [since xy = 1]
= 16
= D

RELATED RESOURCE (video)
- Laws of exponents - part I: https://www.gmatprepnow.com/module/gmat ... video/1025

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed May 25, 2016 4:31 pm

if xy=1 then what is the value of 2^(x+y)Â²/ 2^(x-y)Â²

1)2
2) 4
3) 8
4) 16
5) 32

Alternate Approach.

Since we're told that xy = 1, let's lets x = 1 and y = 1
We get:
2^(x+y)Â²/ 2^(x-y)Â² = 2^(1+1)Â²/ 2^(1-1)Â²
= 2^(2)Â²/2^(0)Â²
= 2â�´/2â�°
= 16/1
= 16
= D

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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