Giải :
1)$\sqrt{x^2+x+5}-\sqrt{x^2-4x+10}=x^2+5x+\frac{45}{4}$
2)$\left\{\begin{matrix} \sum_{i=1}^{2016}\sqrt{1+x_i}=\sqrt{2016.2017}\\ \\ \sum_{i=1}^{2016}\sqrt{1-x_i}=\sqrt{2015.2016} \end{matrix}\right.$
3)$\left\{\begin{matrix} 6x(y^2+z^2)=13yz\\3y(x^2+z^2)=5xz \\ 6z(x^2+y^2)=5xy \end{matrix}\right.$
4)$\left\{\begin{matrix} (2x^2-3x+4)(2y^2-3y+4)=18\\x^2+y^2+xy-7x-6y+14=0 \end{matrix}\right.$
5)$\left\{\begin{matrix} x^3+3x^2+2x-5=y\\y^3+3y^2+2y-5=z \\ z^3+3z^2+2z-5=x \end{matrix}\right.$