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zx - zy - 5x + 5y = z(x - y) - 5(x - y) = (z - 5)(x - y)
x2 - y + x2y - x3 = (x2 - x3) + (x2y - y)
= x2(1 - x) + y(x2 - 1) = -x2(x - 1) + y(x - 1)(x + 1)
= (x - 1)[-x2 + y(x + 1)] = (x - 1)(xy + y - x2)
4x2 - t2 - 4ty - 4y2 = (2x)2 - (t2 + 4ty + 4y2)
= (2x)2 - (t + 2y)2 = (2x - t - 2y)(2x + t + 2y)
4x - x2 - 4 + y2 = y2 - (-4x + x2 + 4) = y2 - (x - 2)2
= (y - x + 2)(y + x - 2)
y2 - x2 - 2x - 1 = y2 - (x2 + 2x + 1) = y2 - (x + 1)2
= (y - x - 1)(y + x + 1)
= -[(x - 2)2 - y2
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May I delete the last row ?