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34dddsf $\{\begin{align} x=-1 \\ x=3 \\ \end{align}$ .werewrew
 \left\{\begin{matrix} x=1\\ x=2 \end{matrix}\right.

$$\begin{aligned} 2x - 4 &= 6 \\ 2x &= 10 \\ x &= 5 \end{aligned}$$ $$\begin{eqnarray} y &=& x^4 + 4 \nonumber \\ &=& (x^2+2)^2 -4x^2 \nonumber \\ &\le&(x^2+2)^2 \nonumber \end{eqnarray}$$