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Mathematics

(a12a)2\Big(a - \dfrac{1}{2a}\Big)^2 is equal to :

  1. (a2+14a22)\Big(a^2 + \dfrac{1}{4a^2} - 2\Big)

  2. (a2+14a2+2)\Big(a^2 + \dfrac{1}{4a^2} + 2\Big)

  3. (a2+14a21)\Big(a^2 + \dfrac{1}{4a^2} - 1\Big)

  4. (a214a22)\Big(a^2 - \dfrac{1}{4a^2} - 2\Big)

Expansions

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Answer

Given,

(a12a)2\Big(a - \dfrac{1}{2a}\Big)^2

Expanding,

(a12a)(a12a)a2a×12a12a×a12a×12aa21212+14a2a2+14a21.\Rightarrow \Big(a - \dfrac{1}{2a}\Big)\Big(a - \dfrac{1}{2a}\Big) \\[1em] \Rightarrow a^2 - a \times \dfrac{1}{2a} - \dfrac{1}{2a} \times a - \dfrac{1}{2a} \times -\dfrac{1}{2a} \\[1em] \Rightarrow a^2 - \dfrac{1}{2} - \dfrac{1}{2} + \dfrac{1}{4a^2} \\[1em] \Rightarrow a^2 + \dfrac{1}{4a^2} - 1.

Hence, Option 3 is the correct option.

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