Question

{x+y=0}
{x-y=4}

x^2-xy=?

Answer 1

x+y=0}{x-y=4}

2x = 4
 x= 2
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x  + y = 0 ==> y = - x ==> y = - 2
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x^2-xy=?

2^2 - 2.(-2)

4 + 4 

8