Question Number 29834 by abdo imad last updated on 12/Feb/18
$${find}\:\:\:\:\frac{\mathrm{1}}{{cos}^{\mathrm{4}} \left(\frac{\pi}{\mathrm{9}}\right)}\:+\frac{\mathrm{1}}{{cos}^{\mathrm{4}} \left(\frac{\mathrm{3}\pi}{\mathrm{9}}\right)}\:+\:\frac{\mathrm{1}}{{cos}^{\mathrm{4}} \left(\frac{\mathrm{5}\pi}{\mathrm{9}}\right)}\:+\frac{\mathrm{1}}{{cos}^{\mathrm{4}} \left(\frac{\mathrm{7}\pi}{\mathrm{9}}\right)}\:. \\ $$
Commented by MJS last updated on 14/Feb/18
$$=\mathrm{1120}\:\mathrm{but}\:\mathrm{it}\:\mathrm{takes}\:\mathrm{quite}\:\mathrm{some} \\ $$$$\mathrm{time}\:\mathrm{to}\:\mathrm{show}... \\ $$