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 9 of 11.
Prasad said:
1 decade ago
(a-b)^2 = a^2+b^2-2ab.
Then 2ab = (a^2+b^2)-(a-b)^2.
2ab = 29-(3)^2.
2ab = 20.
ab = 10.
Then 2ab = (a^2+b^2)-(a-b)^2.
2ab = 29-(3)^2.
2ab = 20.
ab = 10.
Arshiya said:
1 decade ago
If (a-b) = 7 ab = 9, then find the value of (a2+b2)?
Ram said:
1 decade ago
(a+b)^2-(a-b)^2 = 4ab.
Suganya said:
1 decade ago
Sathish said correct solution and take a time shortly to solve the problem.
Krishna said:
1 decade ago
a2+b2=(a-b)(a-b)+2ab hota hi 3*3+2ab=29,2ab=20,ab=10
Krishna said:
1 decade ago
a^2+b^2=(a-b)(a-b)+2ab. Now putting the value of (a-b)we get that 9+2ab=29, 2ab=20, ab=10.
Bhavana said:
1 decade ago
I didn't get the fifth line. Can you explain it.
Vamshi said:
1 decade ago
A-B = 3.
A^2+B^2 = 29.
Squaring on both sides.
(A-B) ^2 = 3^2.
A^2+B^2-2AB = 9.
29-2AB =9.
20 = 2AB.
AB = 10.
A^2+B^2 = 29.
Squaring on both sides.
(A-B) ^2 = 3^2.
A^2+B^2-2AB = 9.
29-2AB =9.
20 = 2AB.
AB = 10.
MANOJ K P said:
1 decade ago
VERY SIMPLE.
A-B = 3.
SQUARE IT BOTH SIDE.
(A-B) ^2 = (3*3).
A^2+B^2-2AB = 9.
2AB = A^2+B^2-9.
WE HAVE A^2+B^2 = 29 APPLY THIS.
2AB = 29-9.
2AB = 20.
AB = 20/2.
AB = 10.
A-B = 3.
SQUARE IT BOTH SIDE.
(A-B) ^2 = (3*3).
A^2+B^2-2AB = 9.
2AB = A^2+B^2-9.
WE HAVE A^2+B^2 = 29 APPLY THIS.
2AB = 29-9.
2AB = 20.
AB = 20/2.
AB = 10.
BOOPATHI said:
1 decade ago
A-B = 3.
A = 3+B.
WE KNOW THAT, A^2+B^2 = 29.
(3+B) ^2+B^2 = 29.
9+B^2+6B+B^2 = 29.
2B^2+6B-20 = 0.
B^2+3B-10 = 0.
SOLVE THIS EQN.
B = 2 & B = -5.
THEN TAKE +VALVE B = 2.
WE KNOW THAT A-B = 3.
SO A-2 = 3.
A = 5.
KNOW FIND.
AB = 2*5 = 10.
A = 3+B.
WE KNOW THAT, A^2+B^2 = 29.
(3+B) ^2+B^2 = 29.
9+B^2+6B+B^2 = 29.
2B^2+6B-20 = 0.
B^2+3B-10 = 0.
SOLVE THIS EQN.
B = 2 & B = -5.
THEN TAKE +VALVE B = 2.
WE KNOW THAT A-B = 3.
SO A-2 = 3.
A = 5.
KNOW FIND.
AB = 2*5 = 10.
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