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by goyalsau » Sat Oct 02, 2010 1:59 pm
If xy = -6 , what is the value of xy(x+y) ?

1)x-y=5

2)xy^2=18
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by shovan85 » Sat Oct 02, 2010 2:06 pm
IMO B
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by goyalsau » Sat Oct 02, 2010 2:23 pm
shovan85 wrote:IMO B

This is How i did with option A

xy = -6 and x-y = 5 Given Required xy(x+y)

x-y = 5
(x-y)^2 = 25
x^2 + y^2 - 2xy = 25
x^2 + y^2 -2( -6 ) = 25
x^2 + y^2 -12 = 25
x^2 + y^2 = 37
x^2 + y^2 + 2xy = 37 +2xy
(x + y ) ^2 = 37 - 12
(x + y ) ^2 = 25

I was doing it like this with the first option But just now i realize that x+y can be +ve and -ve both
So my technique is wrong.
Thanks for quick reply.......
Saurabh Goyal
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by shovan85 » Sat Oct 02, 2010 2:35 pm
goyalsau wrote:
shovan85 wrote:IMO B

This is How i did with option A

xy = -6 and x-y = 5 Given Required xy(x+y)

x-y = 5
(x-y)^2 = 25
x^2 + y^2 - 2xy = 25
x^2 + y^2 -2( -6 ) = 25
x^2 + y^2 -12 = 25
x^2 + y^2 = 37
x^2 + y^2 + 2xy = 37 +2xy
(x + y ) ^2 = 37 - 12
(x + y ) ^2 = 25

I was doing it like this with the first option But just now i realize that x+y can be +ve and -ve both
So my technique is wrong.
Thanks for quick reply.......
Yes because of the opposing signs it cannot be A. Isn.t is B? whats OA?
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by goyalsau » Sat Oct 02, 2010 2:37 pm
you are absolutely right it is B.
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