Let x = tan(y), then 1/x = cot(y). Hence (assuming that atan and acot

return values in the range (-pi/2, pi/2):

y= atan(x) = acot(1/x).

So: acot(x) - atan(1/x) = 0, and so the derivative is zero (the derivative of a constant function is zero).

Also if atan abd acos have the restriction on range we have also proven part B.

RonL