от atnast » 13 Мар 2012, 10:09
[tex]tg3x=tg(2x+x)=\frac{tg2x+tgx}{1-tg2x.tgx}=\frac{\frac{2tgx}{1-tg^{2}x}+tgx}{1-\frac{2tg^{2}x}{1-tg^{2}x}}=\frac{3tgx-tg^{3}x}{1-3tg^{2}x}=tgx\frac{(\sqrt{3}-tgx)(\sqrt{3}+tgx)}{(1+\sqrt{3}tgx)(1-\sqrt{3}tgx)}=[/tex]
[tex]=tgx\frac{(tg60^\circ -tgx)(tg60^\circ+tgx)}{(1+tg60^\circ.tgx)(1-tg60^\circ.tgx)}=tgx.tg(60^\circ-x).tg(60^\circ+x)[/tex]