Question

If xy1 = 0 then prove that x3 y3  1 =3xy

Answer 1

HEY!!

if x+y+1 = 0 then prove that x3 + y3 + 1 =3xy

we know x+y+1=0

then x+y = -1

x+y+1 = 0

(x+y)3 = (-1)3

x3 + y3 +3xy(x+y) = -1

x3 +y3 +3xy(-1) = -1

x3 +y3 - 3xy = -1

x3 + y3 +1 = 3xy

It is proveed

Answer 2

Here is your answer 
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we know x+y+1=0

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            = x+y = -1

            = x+y+1 = 0

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=> (x+y)3 = (-1)3

=> x3 + y3 +3xy(x+y)
=> -1

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=> x3 +y3 +3xy(-1) = -1

=> x3 +y3 - 3xy = -1

=> x3 + y3 +1 = 3xy