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the value of x^4 – y^4

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the value of x^4 – y^4

by sanju09 » Fri Oct 15, 2010 10:15 pm
If x and y are distinct positive integers, what is the value of x^4 - y^4?

[1] (y^2 + x^2) (y + x) (x - y) = 240.

[2] x^y = y^x and x > y.



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Source: — Data Sufficiency |
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by neerajkumar1_1 » Sat Oct 16, 2010 12:59 am
x^4 - y^4 = (x^2-y^2)(x^2+y^2) = (y^2 + x^2) (y + x) (x - y)

statement 1) gives us exactly that...
sufficient

statement 2)

x^y = y^x x>y

now x and y cannot be 2 diff primes..

only way this is possible is
4^2 = 2^4
since x > y
x = 4 and y =2

again
sufficient..

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by ankurmit » Sat Oct 16, 2010 1:31 am
@Neeaj ..Nice explanation about stem B
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