Help with inequality problem 
Given $a$ , $b$ , $c \ge 0$ show that
  $$\frac{a^2}{(a+b)(a+c)} + \frac{b^2}{(b+a)(b+c)}+ \frac{c^2}{(c+a)(c+b)} \ge \frac{3}{4}.$$

I tried using Titu's lemma on it, resulting in 
$$\frac{a^2}{(a+b)(a+c)}+\frac{b^2}{(b+a)(b+c)}+ \frac{c^2}{(c+a)(c+b)}\ge \frac{(a+b+c)^2}{a^2+b^2+c^2 + 3(ab + bc + ca)} $$
And I am stuck here. 

Hint.
As the inequality is homogeneous, making the substitutions $b=\lambda a, c=\mu a$ we have
$$\frac{a^2}{(a+b)(a+c)} + \frac{b^2}{(b+a)(b+c)}+ \frac{c^2}{(c+a)(c+b)} = \frac{\lambda ^2 \mu +\lambda ^2+\lambda  \mu ^2+\lambda +\mu ^2+\mu }{(\lambda +1) (\mu +1) (\lambda +\mu )} = f(\lambda,\mu)
$$
with stationary points as the solutions $(\lambda^*,\mu^*)$ for
$$
\nabla f = 0\Rightarrow \cases{\lambda ^2 \mu -\mu ^2 = 0\\ \lambda ^2-\lambda  \mu ^2=0}
$$
now  discarding the solution $\lambda=0,\mu = 0$ we have to demonstrate that $f(\lambda^*,\mu^*)\ge \frac 34$.
