Question Number 138835 by mathdanisur last updated on 18/Apr/21
$${x}^{\mathrm{3}} −\mathrm{9}{x}+\mathrm{1}=\mathrm{0} \\ $$
Commented by mr W last updated on 18/Apr/21
$${x}_{{k}} =\mathrm{2}\sqrt{\mathrm{3}}\mathrm{sin}\:\left(\frac{\mathrm{1}}{\mathrm{3}}\mathrm{sin}^{−\mathrm{1}} \frac{\sqrt{\mathrm{3}}}{\:\mathrm{18}}+\frac{\mathrm{2}{k}\pi}{\mathrm{3}}\right)\:\:\:{k}=\mathrm{0},\mathrm{1},\mathrm{2} \\ $$
Commented by mathdanisur last updated on 18/Apr/21
$${Thank}\:{Sir} \\ $$
Commented by mathdanisur last updated on 19/Apr/21
$${Where}\:{did}\:{you}\:{get}\:{it}\:{fro}\:{can}\:{you}\:{explain}\:{Sir} \\ $$
Commented by mr W last updated on 19/Apr/21
$${see}\:{Q}\mathrm{89687} \\ $$
Commented by Dwaipayan Shikari last updated on 19/Apr/21
$${Coincidence}\:!\:{same}\:{kind}\:{of}\:{question}\:{asked}\:{in}\:{same}\:{dates}. \\ $$$${One}\:{year}\:{interval}! \\ $$