SSC CGL 11 Aug 2017 Shift 1 Paper

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Question : 63 of 100

Marks: +1, -0

If

( x / y ) + (y / x ) = 1,

then what is the value of

x^ 3 + y ^3

?

-1
0
1
3

Solution:

x / y + y / x = 1

⇒

{x^2+y^2}/{xy}=1

⇒

x ^2 + y ^2 = xy

⇒

x^ 2 + y^2 - x y =0

∴

x^3 + y^ 3 = (x + y ) (x ^2 + y ^2 - xy)

= (x + y )× 0 = 0

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