Răspuns:
Explicație pas cu pas:
[tex]l_{3}^{-2}+l_{4}^{-2}+l_{6}^{-2}=\dfrac{1}{l_{3}^{2}} +\dfrac{1}{l_{4}^{2}}+\dfrac{1}{l_{6}^{2}}= \dfrac{1}{(R\sqrt{3})^{2}}+ \dfrac{1}{(R\sqrt{2})^{2}}+ \dfrac{1}{R^{2}}= \\=\dfrac{^{2)}1}{3R^{2}}+\dfrac{^{3)}1}{2R^{2}}+\dfrac{^{6)}1}{R^{2}}=\dfrac{2+3+6}{6R^{2}}=\dfrac{11}{6*(\sqrt{11})^{2} }=\dfrac{11}{6*11}=\dfrac{1}{6}[/tex]
