equation: x^2 + 4cx/(1+c^2) +1 = 0
gradient of log(1+x^2) a x=c is y' = 2c / (1+c^2)
Show that delta = -4 (1-c^2 / 1+c^2)^2 for this quadratic, and hence that the only tangents to y = log (1+x^2) which are mutually perpendicular are those at x= -1 and x= 1.
skip the show part and help me...