Factorise $a^{2} + \dfrac{1}{a^{2}} + 2$ (for $a \ne 0$).

Factorise $a^{2} + \dfrac{1}{a^{2}} + 2$ (for $a \ne 0$).
  1. $\left(a + \dfrac{1}{a}\right)^{2}$
  2. $\left(a - \dfrac{1}{a}\right)^{2}$
  3. $\left(a + \dfrac{1}{a}\right)\left(a - \dfrac{1}{a}\right)$
  4. $\dfrac{a^{2}+1}{a^{2}}$

Solution

$a^{2}+\dfrac{1}{a^{2}}+2 = a^{2}+2 \cdot a \cdot \dfrac{1}{a}+\left(\dfrac{1}{a}\right)^{2} = \left(a+\dfrac{1}{a}\right)^{2}$.

Asked in: IMO

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