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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Quadratic Equation

NDA 2025 · Mathematics · Quadratic Equation

If x = (1111)_2 , y = (1001)_2 and z = (110)_2 , then what is x^3 -...

If x=(1111)2x = (1111)_2, y=(1001)2y = (1001)_2 and z=(110)2z = (110)_2, then what is x3−y3−z3−3xyzx^3 - y^3 - z^3 - 3xyz equal to?

Options

  1. A(1111001)2(1111001)_2
  2. B(1001111)2(1001111)_2
  3. C(1)2(1)_2
  4. D(0)2(0)_2

Correct answer

D. (0)2(0)_2

Step-by-step solution

Converting the given binary numbers to decimal:

x=(1111)2=1×23+1×22+1×21+1×20=15x = (1111)_2 = 1 \times 2^3 + 1 \times 2^2 + 1 \times 2^1 + 1 \times 2^0 = 15

y=(1001)2=1×23+0×22+0×21+1×20=9y = (1001)_2 = 1 \times 2^3 + 0 \times 2^2 + 0 \times 2^1 + 1 \times 2^0 = 9

z=(110)2=1×22+1×21+0×20=6z = (110)_2 = 1 \times 2^2 + 1 \times 2^1 + 0 \times 2^0 = 6

Observing the relationship between xx, yy, and zz:

y+z=9+6=15=xy + z = 9 + 6 = 15 = x

⇒x−y−z=0\Rightarrow x - y - z = 0

Using the algebraic identity, if a+b+c=0a + b + c = 0, then a3+b3+c3−3abc=0a^3 + b^3 + c^3 - 3abc = 0.

Substituting a=xa = x, b=−yb = -y, and c=−zc = -z:

x+(−y)+(−z)=0x + (-y) + (-z) = 0

⇒x3+(−y)3+(−z)3−3(x)(−y)(−z)=0\Rightarrow x^3 + (-y)^3 + (-z)^3 - 3(x)(-y)(-z) = 0

⇒x3−y3−z3−3xyz=0\Rightarrow x^3 - y^3 - z^3 - 3xyz = 0

In binary representation, 00 is (0)2(0)_2.

Answer: (0)2(0)_2
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