2xy x is 2 y is 7 therefore (2)(2)(7) = 28
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(x - y)2 >= 0 since the left hand side is a square. ie x2 - 2xy + y2 >= 0 so x2 + y2 >= 2xy
(2x2+4xy-3)-(x2-2xy-4)Answer: x2+6x+1
x2 + y2 = x2 - 2xy + y2 + 2xy = (x - y)2 + 2xy = 72 + 2*8 = 49 + 16 = 65 You could, instead, solve the two equations for x and y and substitute, but the above method is simpler.
(x + y)2 = x2 + 2xy + y2
(x - y - z)(x - y + z)