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Mathematics

The value of the discriminant of the equation, x2 - (2\sqrt{2} + 1)x + 2\sqrt{2} = 0 is:

  1. 3 + 222\sqrt{2}

  2. 1 - 222\sqrt{2}

  3. 3 - 222\sqrt{2}

  4. 2 - 2\sqrt{2}

Quadratic Equations

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Answer

Comparing x2 - (2\sqrt{2} + 1)x + 2\sqrt{2} = 0 with ax2 + bx + c = 0 we get,

a = 1, b = -(2\sqrt{2} + 1) and c = 2\sqrt{2}.

We know that,

D=b24ac=[(2+1)]24×1×(2)=(2)2+2×2×1+124(2)=2+22+142=322.\Rightarrow D = b^2 - 4ac \\[1em] = [-(\sqrt{2} + 1)]^2 - 4 \times 1 \times (\sqrt{2}) \\[1em] = (\sqrt2)^2 + 2 \times \sqrt2 \times 1 + 1^2 - 4(\sqrt{2}) \\[1em] = 2 + 2\sqrt2 + 1 - 4\sqrt{2} \\[1em] = 3 - 2\sqrt2.

Hence, option 3 is the correct option.

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