If x=(1111)_{2}, y=(1001)_{2} and z=(110)_{2}, then what is x^{3}-y^{3}-z^{3}-3xyz equal to?

  1. A. (1111001)_{2}
  2. B. (1001111)_{2}
  3. C. (1)_{2}
  4. D. (0)_{2}

Correct Answer: D. (0)_{2}

Explanation

x = 15, y = 9, z = 6 in decimal. Since x = y + z, we have x + (-y) + (-z) = 0. The expression is x^3 + (-y)^3 + (-z)^3 - 3x(-y)(-z), which is identically 0 when the sum of variables is 0.

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