Mr0

$\left\{\begin{matrix}
x^{2}+y^{2}+x=1\\
5=\frac{4x^{2}+y^{2}+2xy}{x+y-1}
\end{matrix}\right.$

$\left\{\begin{matrix}
x^{4}-4x^{2}+y^{2}-6y+9=0\\
x^{2}y+x^{2}+2y-22=0
\end{matrix}\right.$

$\left\{\begin{matrix}
y^{3}=x^{3}(9-x^{3})\\
x^{2}y+y^{2}=6x
\end{matrix}\right.$

cosx(2+cos4x)+cos2x-cos3x=0

Cho số phức z₁,z₂,z₃ : $\left | z_{1} \right |=\left | z_{2} \right |=\left | z_{3} \right |=1$
CMR: $\left | z_{1}z_{2}+z_{2}z_{3}+z_{3}z_{1} \right |=\left | z_{1}+z_{2}+z_{3} \right |$