y= tg (x+45°) = tg (x-45°)
Tangente da soma
tg(a + b) = (tg(a) + tg(b))/(1 - tg(a)*tg(b))
tg (x+45°) = (tg(x) + tg(45°))/(1 - tg(x)*tg(45°)) = (tg(x) + 1)/(1 - tg(x))
Tangente da diferença
tg(a - b) = (tg(a) - tg(b))/(1 + tg(a)*tg(b))
tg(x - 45°) = (tg(x) - tg(45°))/(1 + tg(x)*tg(45°)) = (tg(x) - 1)/(1 + tg(x))
y = (tg(x) - 1)/(1 + tg(x))
y = (1/2 - 1)/(1 + 1/2) = (-1/2)/(3/2) = -1/3