Với mọi x ta có :
\(\left(x+1\right)^4\ge0\)
\(\Leftrightarrow\left(x+4\right)^4+\dfrac{1}{2}\ge\dfrac{1}{2}\)
\(\Leftrightarrow A\ge\dfrac{1}{2}\)
Dấu "=" xảy ra khi :
\(\left(x+1\right)^4=0\)
\(\Leftrightarrow x+1=0\)
\(\Leftrightarrow x=-1\)
Vậy \(Min_A=\dfrac{1}{2}\Leftrightarrow x=-1\)
