lim{x->0} (sqrt(x + 4) - 2)/x [*(sqrt(x + 4) + 2)/(sqrt(x + 4) + 2)]
lim{x->0} [(sqrt(x + 4) - 2)*(sqrt(x + 4) + 2)]/[x*(sqrt(x + 4) + 2)] =
lim{x->0} (sqrt(x + 4)^2 - 4)/[2x + sqrt(x^2 * (x + 4))] =
lim{x->0} (x + 4 - 4)/[2x + sqrt(4x^2 * (x/4 + 1))] =
lim{x->0} x/[2x + 2x*sqrt(x/4 + 1)]
lim{x->0} sqrt(x/4 + 1) = 1
lim{x->0} x/[2x + 2x*sqrt(x/4 + 1)] =
lim{x->0} x/(2x + 2x) = 1/4
