>>5
lim(x→a){(x^2F(x)-a^2F(a))/(x^2-a^2)}
=lim(x→a){(x^2F(x)-x^2F(a)+x^2F(a)-a^2F(a))/(x^2-a^2)}
=lim(x→a){x^2/(x+a)}*{(F(x)-F(a))/(x-a)} + F(a)
={a^2/(2a)}*F '(a) + F(a)
=(a/2)F '(a) + F(a)