Question Number 173002 by Mikenice last updated on 04/Jul/22
Commented by kaivan.ahmadi last updated on 05/Jul/22
$$\mathrm{1}−{tg}^{\mathrm{2}} \theta=\mathrm{1}−\frac{{sin}^{\mathrm{2}} \theta}{{cos}^{\mathrm{2}} \theta}=\frac{{cos}^{\mathrm{2}} \theta−{sin}^{\mathrm{2}} \theta}{{cos}^{\mathrm{2}} \theta}= \\ $$$$\frac{\mathrm{1}−\mathrm{2}{sin}^{\mathrm{2}} \theta}{\mathrm{1}−{sin}^{\mathrm{2}} \theta}=\frac{\mathrm{1}−\mathrm{2}\left(\frac{{a}−{b}}{{a}+{b}}\right)^{\mathrm{2}} }{\mathrm{1}−\left(\frac{{a}−{b}}{{a}+{b}}\right)^{\mathrm{2}} }=\frac{\left({a}+{b}\right)^{\mathrm{2}} −\mathrm{2}\left({a}−{b}\right)^{\mathrm{2}} }{\left({a}+{b}\right)^{\mathrm{2}} −\left({a}−{b}\right)^{\mathrm{2}} }= \\ $$$$\frac{−{a}^{\mathrm{2}} +\mathrm{6}{ab}−{b}^{\mathrm{2}} }{\mathrm{4}{ab}} \\ $$
Answered by CElcedricjunior last updated on 05/Jul/22