Răspunsuri

2014-10-01T20:46:35+03:00
Folosim formulele:

(a+b)^3=a^3+b^3+3ab(a+b)

(a-b)(a+b)=a^2-b^2

\sqrt[3]{x^3}=x

Ridicam la puterea a treia fiecare membru al egalitatii si obtinem o egalitate echivalenta:

9+\sqrt{80}+9-\sqrt{80}+3\sqrt[3]{9^2-80}(\sqrt[3]{9+\sqrt{80}}+\sqrt[3]{9-\sqrt{80}})=3^3

18+3\cdot1\cdot3=27

27=27