Ta có: \(y=g\left(x\right)=4x^2+1\)
a) \(y=g\left(-1\right)=4\left(-1\right)^2+1=4.1+1=4+1=5\)
\(y=g\left(-2\right)=4\left(-2\right)^2+1=4.2^2+1=4.4+1=16+1=17\)
b) \(y=g\left(x\right)=4x^2+1=5\)
\(\Rightarrow4x^2=5-1\)
\(\Rightarrow4x^2=4\)
\(\Rightarrow x^2=4:4\)
\(\Rightarrow x^2=1\)
\(\Rightarrow\left[{}\begin{matrix}x=1\\x=-1\end{matrix}\right.\)
Vậy nếu \(g\left(x\right)=5\) thì \(x=1\) hoăc \(x=-1\)
c) \(y=4x^2+1\)
\(\Leftrightarrow y=\left(2x\right)^2+1\ge1\)
Vậy GTLN của \(y=1\) khi \(2x=0\Leftrightarrow x=0\)
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