Bài $8$.
$1$) `(2a+1)^2 + (b+3)^4 + (5c-6)^2 ≤ 0`
Vì : `(2a+1)^2 + (b+3)^4 + (5c-6)^2 ≥ 0` `∀` `a;b;c`
$⇒$ `(2a+1)^2 = (b+3)^4 = (5c-6)^2=0`
`⇒` $\left\{\begin{matrix}2a + 1 = 0 & \\b + 3 = 0 &\\ 5c - 6 = 0\end{matrix}\right.$
$⇒$ $\left\{\begin{matrix}a = \dfrac{-1}{2} & \\b = - 3 &\\ c = \dfrac{6}{5}\end{matrix}\right.$
Vậy `(a;b;c)=(-1/2;-3;6/5)`