Derivatives Elasticity
1. **State the problem:** We are given the function $y = x^2 e^{2x}$ and need to find the first derivative $y'$, the second derivative $y''$, and then calculate the price elasticity of demand $E = \frac{dy/dx \cdot x}{y}$.
2. **First derivative $y'$:** Use the product rule: If $y = u \cdot v$, then $y' = u'v + uv'$. Here, $u = x^2$ and $v = e^{2x}$.
- Compute $u' = 2x$.
- Compute $v' = \frac{d}{dx}e^{2x} = 2 e^{2x}$.
- Apply product rule:
$$y' = (2x)e^{2x} + x^2 (2 e^{2x}) = 2x e^{2x} + 2x^2 e^{2x} = 2x e^{2x}(1 + x).$$
3. **Second derivative $y''$:** Differentiate $y' = 2x e^{2x}(1 + x)$. Again use product rule treating $w = 2x(1+x)$ and $z = e^{2x}$.
- Simplify $w = 2x + 2x^2$.
- Compute $w' = 2 + 4x$.
- Compute $z' = 2 e^{2x}$.
- Then:
$$y'' = w' z + w z' = (2 + 4x)e^{2x} + (2x + 2x^2)(2 e^{2x}) = e^{2x} (2 + 4x) + 2 e^{2x}(2x + 2x^2).$$
- Factor $e^{2x}$ out:
$$y'' = e^{2x} [2 + 4x + 4x + 4x^2] = e^{2x} (2 + 8x + 4x^2).$$
4. **Price elasticity of demand $E$:** Defined as
$$E = \frac{dy/dx \cdot x}{y} = \frac{y' x}{y}.$$
Plug in expressions:
$$E = \frac{(2x e^{2x}(1+x)) x}{x^2 e^{2x}} = \frac{2x^2 e^{2x} (1+x)}{x^2 e^{2x}} = 2 (1 + x).$$
5. **Final answers:**
- First derivative: $$y' = 2x e^{2x}(1 + x).$$
- Second derivative: $$y'' = e^{2x}(2 + 8x + 4x^2).$$
- Price elasticity of demand: $$E = 2 (1 + x).$$