i cant really be stuffed doing Q3c.ii) with out the right lettering and such so i'll do Q5biii.
To find the inverse (f-¹(x)), you need to change y into x and x into y, hence
original eqn = y = 1/(1+x²)
thus new eqn = x = 1/(1+y²)
which = x(1+y²) = 1
= y² = 1/x - 1
= y = sqrt(1/x -1)
= y= sqrt ((1-x)/x) = inverse of f(x)