Răspuns:
[tex]{(a + \frac{1}{a} ) }^{2} = {a}^{2} + 2 + \frac{1}{ {a}^{2} } = 23 + 2 = 25[/tex]
deci
[tex] ({a + \frac{1}{a} })^{2} = \sqrt{25} = 5[/tex]
analog
[tex]( {a - \frac{1}{a} })^{2} = \sqrt{21} [/tex]
