Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 03 Jul 2015, 19:26

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# What is the value of a^4 - b^4? 1) a^2 - b^2 = 16 2) a + b =

Author Message
TAGS:
Director
Joined: 01 May 2007
Posts: 794
Followers: 1

Kudos [?]: 127 [0], given: 0

What is the value of a^4 - b^4? 1) a^2 - b^2 = 16 2) a + b = [#permalink]  25 Nov 2007, 15:06
00:00

Difficulty:

(N/A)

Question Stats:

100% (01:02) correct 0% (00:00) wrong based on 1 sessions
What is the value of a^4 - b^4?

1) a^2 - b^2 = 16
2) a + b = 8
VP
Joined: 09 Jul 2007
Posts: 1108
Location: London
Followers: 6

Kudos [?]: 76 [0], given: 0

Re: DS: Exponents! [#permalink]  25 Nov 2007, 16:38
jimmyjamesdonkey wrote:
What is the value of a^4 - b^4?

1) a^2 - b^2 = 16
2) a + b = 8

1. a^2-b^2=16
a^2=16+b^2 not suff.

2. a=8-b
a^2=64-16b+b^2 not suff.

combined

16+b^2=64-16b+b^2

16b=48
b=3

a=5

C

any other inputs
Director
Joined: 01 May 2007
Posts: 794
Followers: 1

Kudos [?]: 127 [0], given: 0

Can you explain why I can't just take statement #1 and square each term:

a^2-b^2=16

(a^2)^2 - (b^2)^2 = 16^2?

I thought that would give me: a^4 - b^4 = 16^4

You are correct with C.
SVP
Joined: 01 May 2006
Posts: 1798
Followers: 8

Kudos [?]: 102 [0], given: 0

jimmyjamesdonkey wrote:
Can you explain why I can't just take statement #1 and square each term:

a^2-b^2=16

(a^2)^2 - (b^2)^2 = 16^2?

I thought that would give me: a^4 - b^4 = 16^4

You are correct with C.

We cannot do so .... It is missing a term and the sign is wrong.

x-y = 2
=> (x-y)^2 = 2^2
<=> x^2 - 2*x*y + y^2 = 4

... the power of 2 is not distributive as a multiplication is
Similar topics Replies Last post
Similar
Topics:
What is the value of a^2 - b^2? 5 02 May 2013, 09:11
5 What is the value of a - b? (1) a = b + 4 (2) (a - b)^2 = 1 7 30 Aug 2010, 13:52
What is the value of a^4 - b^4? (1) a^2 - b^2 = 16 (2) a + b 6 23 Aug 2007, 16:55
What is the value of a^4 - b^4 ? 1) a^2 - b^2 = 16 2) a+b = 2 22 Dec 2006, 08:20
a#=a^2+2, what is the value of b#? 1. (b-1)#=3 2. (b+2)#=6 2 10 Dec 2005, 05:09
Display posts from previous: Sort by