(1)
Square root of A^2 - B^2 is NOT equal to A-B! In fact, it has nothing to do with A-B.
As you do know yourself, (A-B)(A-B) = A^2 - 2AB + B^2, not simply A^2 - B^2
(2) A^2 - 2AB + B^2 =1
From this we can deduce either of the following:
(A-B)(A-B) = 1
or (B-A)(B-A) = 1
If the former is true, then A-B=1; if the latter is true, then A-B=-1
So statement 2 alone is not sufficient either.
Looking at the 2 statements together, you can play around a little but you will not arrive at a definite answer for A-B.
Kaplan DS
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
Yesdavy420 wrote:Sorry but I am still confused
I understand that (A-B)(A-B) = A^2 - 2AB + B^2 but doesn't
(A-B)(A-B) = (A-B)^2 or A^2 - B^2 if you simplifed it.
(A-B)(A-B) = (A-B)^2
but
(A-B)^2 != A^2 - B^2
rather
(A-B)^2 = A^2 + B^2 - 2AB
You can verify by multiplying (A-B) with (A-B)
Sorry im still confused. thanks
-
cramya
- Legendary Member
- Posts: 2467
- Joined: Thu Aug 28, 2008 6:14 pm
- Thanked: 331 times
- Followed by:11 members
(1)a^2-b^2 = (a+b) (a-b)
a+b = 4
a-b= 9/4
a=25/8
b= 7/8
or
a + b = 3
a - b = 3
a=3 b=0
We cannot come up with a definite value for a-b INSUFFICIENT
For (2)
(A-B) (A-B) = 1
A-B CAN BE EQUAL TO -1 OR 1
INSUFFICIENT
Taking both together still INSUFFICIENT(we cannot come to a definite value
HENCE E
a+b = 4
a-b= 9/4
a=25/8
b= 7/8
or
a + b = 3
a - b = 3
a=3 b=0
We cannot come up with a definite value for a-b INSUFFICIENT
For (2)
(A-B) (A-B) = 1
A-B CAN BE EQUAL TO -1 OR 1
INSUFFICIENT
Taking both together still INSUFFICIENT(we cannot come to a definite value
HENCE E
davy420 wrote:Can somebody help me understand this question
What is the value of A-B
1) A^2 - B^2 = 9
2) A^2 - 2AB + B^2 =1
from 1
(a-b)(a+b) = 9 thus a-b can = -3 0r 3...insuff
from 2
(A-B)(A-B) = 1 a-b can =1 or -1...insuff
both
no common roots...E
