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by sanju09 » Wed Feb 17, 2010 6:16 am
What is x^8 - y^8 equal to?

(1) x^2 + y^2 = 4.

(2) x^2 - y^2 = 0.
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by ajith » Wed Feb 17, 2010 6:57 am
sanju09 wrote:What is x^8 - y^8 equal to?

(1) x^2 + y^2 = 4.

(2) x^2 - y^2 = 0.
x^8 - y^8 = (x^4+y^4)( x^2 - y^2) (x^2 + y^2)

1) is not sufficient; we have to find out (x^4+y^4) and ( x^2 - y^2)
2) is sufficient since x^8 - y^8 = (x^4+y^4)( x^2 - y^2) (x^2 + y^2)
if x^2 - y^2 = 0, x^8 - y^8=0

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by shashank.ism » Wed Feb 17, 2010 12:41 pm
sanju09 wrote:What is x^8 - y^8 equal to?

(1) x^2 + y^2 = 4.

(2) x^2 - y^2 = 0.
St.1: x^2 + y^2 = 4. two unknowns can't get x and y
also x^8 - y^8 =(x^4+y^4)( x^4-y^4))=(x^4+y^4)( x^2-y^2) (x^2+y^2)so can't get to ans anywayy

St.2: x^2 - y^2 = 0 --> x=+/- y --> x^8 = y^8 --> x^8 - y^8 =0 so sufficient.......

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