Question

Tot așa!cred :)))
Dau 5*

Answer 1

$\dfrac{\text{tg}\,a +\text{tg}\,b}{\text{tg}(a+b)} -\dfrac{\text{tg}\,a -\text{tg}\,b}{\text{tg}(a-b)} =\\ \\ = \dfrac{\text{tg}\,a +\text{tg}\,b}{\dfrac{\text{tg}\,a +\text{tg}\,b}{1-\text{tg}\,a\,\text{tg}\,b}} - \dfrac{\text{tg}\,a -\text{tg}\,b}{\dfrac{\text{tg}\,a -\text{tg}\,b}{1+\text{tg}\,a\,\text{tg}\,b}}\\ \\ =1-\text{tg}\,a\, \text{tg}\,b - (1+\text{tg}\,a\,\text{tg}\,b)\\ \\= 1-\text{tg}\,a\, \text{tg}\,b-1-\text{tg}\,a\, \text{tg}\,b\\ \\ = -2\,\text{tg}\,a\, \text{tg}\,b$