Question Number 174424 by mnjuly1970 last updated on 31/Jul/22
$$ \\ $$$$\:\:\:\:#\:\:{prove}\:\:{that}\:\:# \\ $$$$\:\:\:{tan}^{\:\mathrm{2}} \left(\:\mathrm{10}^{\:\mathrm{o}} \right)\:+\:{tan}^{\:\mathrm{2}} \left(\mathrm{50}^{\:\mathrm{o}} \:\right)+{tan}^{\:\mathrm{2}} \left(\mathrm{70}^{\:\mathrm{o}} \right)\overset{?} {=}\:\mathrm{9} \\ $$$$\:\:\:\:\:−−−−− \\ $$$$ \\ $$