Aptitude - Simplification - Discussion
Discussion Forum : Simplification - General Questions (Q.No. 4)
4.
If a - b = 3 and a2 + b2 = 29, find the value of ab.
Answer: Option
Explanation:
2ab = (a2 + b2) - (a - b)2
= 29 - 9 = 20
ab = 10.
Discussion:
107 comments Page 1 of 11.
Satish said:
1 decade ago
Actually (a-b)^2 = a^2 - 2ab + b^2 substitute in above formula we can get the answer.
Kumar said:
1 decade ago
It's correct.
Sharmila said:
1 decade ago
@Satish is correct this is easy.
Rachana said:
1 decade ago
Please explain the formula in explanation.
Nagendramurthy said:
1 decade ago
=(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..
=(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..
(1)
Vishnu dilip said:
1 decade ago
Easy method
Given
a - b = 3 and a*a - b*b = 3,
So,
a = 5 and b= 2,
So,
ab = 5*2 = 10
Given
a - b = 3 and a*a - b*b = 3,
So,
a = 5 and b= 2,
So,
ab = 5*2 = 10
Myself said:
1 decade ago
(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.
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.
Pritam das said:
1 decade ago
(a-b)^2+2ab=29
or,(3)^2+2ab=29
or,9+2ab=29
or,2ab=20
or,ab=10
or,(3)^2+2ab=29
or,9+2ab=29
or,2ab=20
or,ab=10
Akash said:
1 decade ago
In a2+b2=29.
substract both side by 2ab.
substract both side by 2ab.
Sunita said:
1 decade ago
Where did 9 come from?
How did we arrive at 29-9?
How did we arrive at 29-9?
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