Giải:
a) \(A=17-\left(x+4\right)^2\le17;\forall x\)
\(\Leftrightarrow A_{Max}=17\)
\("="\Leftrightarrow x+4=0\Leftrightarrow x=-4\)
Vậy ...
b) \(B=-x^2+8x+152\)
\(\Leftrightarrow B=-x^2+8x-16+168\)
\(\Leftrightarrow B=-\left(x^2-8x+16\right)+168\)
\(\Leftrightarrow B=-\left(x-4\right)^2+168\)
\(\Leftrightarrow B=168-\left(x-4\right)^2\le168;\forall x\)
\(\Leftrightarrow B_{Max}=168\)
\("="\Leftrightarrow x-4=0\Leftrightarrow x=4\)
Vậy ...
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