`Q = (2x-4)^6 + (y-7)^{12} - 21`
Vì : `(2x-4)^6;(y-7)^{12}` $≥$ $0$ $∀$ $x;y$
$⇒$ `Q ≥ 0 + 0 -21 = -21`
Dấu " $=$ " khi : $(2x-4)^6 = (y-7)^{12} = 0$
$⇒$ $\left\{\begin{matrix}2x-4=0 & \\ y-7=0& \end{matrix}\right.$
$⇒$ $\left\{\begin{matrix}x=2 & \\ y=7& \end{matrix}\right.$
Vậy `Q` đạt $GTNN=-21$ khi `(x;y)=(2;7)`