[tex]a)\\\\ (x)=x^6-8=(x^2)^3-2^3=(x^2 - 2)(x^4 + 2x^2 + 4)=(x-\sqrt2)(x+\sqrt2)(x^4 + 2x^2 + 4)\\\\x-\sqrt2=0\ \ \ lub\ \ \ x+\sqrt2=0\\\\x=\sqrt2\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x=-\sqrt2[/tex]
[tex]b)\\\\ (x)=81-x^8=9^2-(x^4)^2=(9-x^4)(9+x^4)=(3-x^2)(3+x^2)(9+x^4)=\\\\(\sqrt3-x)(\sqrt3+x)(3+x^2)(9+x^4)\\\\\sqrt3-x=0\ \ \ lub\ \ \ \sqrt3+x=0\\\\x=\sqrt3\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x=-\sqrt3[/tex]
