Question

Решите пож 3).........

Answer 1

$(a- frac{1}{a}) ^{2}$=$a^{2} + frac{1}{a^2} +2*a* frac{1}{a}$=$(a^{2}+ frac{1}{a^2} )+2$
$a^{2}+ frac{1}{a^2}$=$(a+ frac{1}{a} )^{2}$-2
$a^{2}+ frac{1}{a^2}$=9-2=7