Aptitude - Simplification - Discussion
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Read more:"I never think of the future. It comes soon enough."
- Albert Einstein
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If a - b = 3 and a2 + b2 = 29, find the value of ab.
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10 | [B]. |
12 | | [C]. |
15 | [D]. |
18 |
Answer: Option A
Explanation:
2ab = (a2 + b2) - (a - b)2
= 29 - 9 = 20
 ab = 10.
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Satish said:
(Mon, Sep 6, 2010 12:54:06 PM)
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| Actually (a-b)^2 = a^2 - 2ab + b^2 substitute in above formula we can get the answer. |
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Kumar said:
(Tue, Dec 28, 2010 04:16:04 AM)
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| It's correct. |
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Sharmila said:
(Fri, Mar 25, 2011 03:37:26 AM)
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| @Satish is correct this is easy. |
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Rachana said:
(Wed, May 25, 2011 08:24:22 AM)
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| Please explain the formula in explanation. |
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Nagendramurthy said:
(Fri, Jun 17, 2011 04:11:50 AM)
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=(a2+b2)-(a-b)2
=(a2+b2)-(a2-2ab+b2)
removing brackets
=a2+b2-a2+2ab-b2
hence we get 2ab
therefore
2ab=(a2+b2)-(a-b)2
they have given the value of a2+b2=29 and a-b=3. substituting the value
2ab= 29-(3)2
=29-3*3
=29-9
2ab=20
ab=20/2
ab=10
I think you got me.. have a nice day.. |
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Vishnu Dilip said:
(Sun, Aug 7, 2011 07:19:02 PM)
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Easy method
Given
a - b = 3 and a*a - b*b = 3,
So,
a = 5 and b= 2,
So,
ab = 5*2 = 10 |
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Myself said:
(Mon, Aug 8, 2011 11:02:09 PM)
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(a-b)2= a2+b2-2ab..................{eq 1}
it is given that:(a-b)=3,a2+b2=29.
so put it in {eq 1},we get:
3*3=29-2ab.
9=29-2ab.
2ab=29-9
2ab=20
ab=10. |
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Pritam Das said:
(Tue, Aug 9, 2011 09:48:15 PM)
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(a-b)^2+2ab=29
or,(3)^2+2ab=29
or,9+2ab=29
or,2ab=20
or,ab=10 |
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Akash said:
(Sat, Oct 22, 2011 04:13:47 PM)
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In a2+b2=29.
substract both side by 2ab. |
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Sunita said:
(Thu, Nov 24, 2011 07:33:54 PM)
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Where did 9 come from?
How did we arrive at 29-9? |
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Kavi said:
(Thu, Dec 1, 2011 09:50:05 PM)
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a-b=3 and a2+b2=29
b=a-3 sub in above equ,
a2+(a-3)2=29
a2+a2-6a+9=29
a2-3a-10=0
a=5 or -2
let we taken a=5
5^2+b2=29
25+b2=29
b=2
ab=(5)(2)
ab=10 |
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