Resposta :
tg(x + π/4) = -cotg(x)
tg(x) = -1/tg(x + π/4)
tg(2x) = 2tg(x)/(1 - tg²(x) = (-2/tg(x + π/4))/(1 - 1/tg²(x + π/4)) =
tg(2x) = -2tg(x + π/4)/(tg²(x + π/4) - 1)
se tg (x +pi/4)=3, então tg 2x é igual a?
tg(x + π/4) = -cotg(x)
tg(x) = -1/tg(x + π/4)
tg(2x) = 2tg(x)/(1 - tg²(x) = (-2/tg(x + π/4))/(1 - 1/tg²(x + π/4)) =
tg(2x) = -2tg(x + π/4)/(tg²(x + π/4) - 1)