6.014. $\frac{4}{x^{2}+4}+\frac{5}{x^{2}+5}=2$.
## Solution.

Domain: $x \in R$.

$\frac{2 x^{4}+9 x^{2}}{\left(x^{2}+4\right)\left(x^{2}+5\right)}=0 \Leftrightarrow 2 x^{4}+9 x^{2}=0 \Leftrightarrow x^{2}\left(2 x^{2}+9\right)=0$,

$x^{2}=0, x_{1}=0$ or $2 x^{2}+9=0, x_{2,3} \in \varnothing$.

Answer: $x=0$.