\(\displaystyle f(x) \ = \ x^5-81x \ = \ x(x^4-81), \ \implies \ x \ = \ 0, \ x \ = \ \pm3\)
\(\displaystyle Hence, solutions \ are \ (0,0),(-3,0),(3,0)\)
\(\displaystyle Note: \ Descartes' \ Rule \ of \ Signs, \ to \ wit:\)
\(\displaystyle f(x) \ = \ x^5-81x, \ one \ change, \ f(-x) \ = \ -x^5+81x, \ one \ change, \ ergo \ only \ possibility \ is\)
\(\displaystyle -+ 0 \ \ I\)
\(\displaystyle 1 \ \ 1 \ 1 \ \ 2\)
\(\displaystyle As \ far \ as \ Newton's \ Method \ goes, \ have \ fun.\)
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