Construct one function of the form \(h(x)=ae^{g(x)}+c\), where \(g\) is a polynomial and \(a,c\in\mathbb{R}\), whose graph has all three properties:
- symmetry about the y-axis,
- horizontal asymptote \(y=1\), and
- a local minimum at \((0,-1)\).
State your choices of \(a\), \(c\), and \(g(x)\), and verify the properties.
Hints
- The vertical shift determines the horizontal asymptote.
- Choose an even polynomial exponent for y-axis symmetry.
- Make the exponent approach \(-\infty\) at both ends.
- Use the given point to determine the remaining coefficient.
Solution
1. Choose \(c=1\) so that \(y=1\) can be the horizontal asymptote.
2. Choose the even polynomial \(g(x)=-x^2\). Then \(g(x)\to-\infty\) as \(x\to\pm\infty\), so \(e^{g(x)}\to0\), and the resulting function is even.
3. Since \(g(0)=0\), the condition \(h(0)=-1\) gives \(a+1=-1\), so \(a=-2\).
4. One valid function is \(h(x)=-2e^{-x^2}+1\). It is even, approaches \(1\) as \(x\to\pm\infty\), and satisfies \(h(0)=-1\).
5. Since \(e^{-x^2}\le1\) for every real \(x\), \(-2e^{-x^2}+1\ge-1\), with equality at \(x=0\). Therefore, \((0,-1)\) is a local minimum (in fact, a global minimum).
Answer
One valid choice is \(a=-2\), \(c=1\), and \(g(x)=-x^2\), giving \(h(x)=-2e^{-x^2}+1\).