Derivatives Exercise 34045B
1. **Statement of the problem:**
Calculate the derivatives of the following functions:
$$f_1(x) = 2x \sqrt{-3x + 2}$$
$$f_2(x) = (-x + 4) e^{-x}$$
$$f_3(x) = \frac{\ln(x^2 + 1)}{x^2 + 1}$$
$$f_4(x) = -x + 7 + 6 \ln(2x + 1) - 6 \ln(2x + 2)$$
$$f_5(x) = \frac{5^x}{5^{2x - 1}}$$
2. **Formulas and rules used:**
- Derivative of product: $\frac{d}{dx}[uv] = u'v + uv'$
- Derivative of quotient: $\frac{d}{dx}\left[\frac{u}{v}\right] = \frac{u'v - uv'}{v^2}$
- Derivative of $\sqrt{g(x)} = \frac{g'(x)}{2\sqrt{g(x)}}$
- Derivative of $e^{g(x)} = e^{g(x)} g'(x)$
- Derivative of $\ln(g(x)) = \frac{g'(x)}{g(x)}$
- Derivative of $a^x = a^x \ln(a)$
3. **Step-by-step solutions:**
**For $f_1(x) = 2x \sqrt{-3x + 2}$:**
- Let $u = 2x$, $v = \sqrt{-3x + 2} = (-3x + 2)^{1/2}$
- $u' = 2$
- $v' = \frac{1}{2}(-3x + 2)^{-1/2} \cdot (-3) = -\frac{3}{2\sqrt{-3x + 2}}$
- Using product rule:
$$f_1'(x) = u'v + uv' = 2 \sqrt{-3x + 2} + 2x \left(-\frac{3}{2\sqrt{-3x + 2}}\right) = 2 \sqrt{-3x + 2} - \frac{3x}{\sqrt{-3x + 2}}$$
**For $f_2(x) = (-x + 4) e^{-x}$:**
- Let $u = -x + 4$, $v = e^{-x}$
- $u' = -1$
- $v' = -e^{-x}$
- Using product rule:
$$f_2'(x) = u'v + uv' = (-1) e^{-x} + (-x + 4)(-e^{-x}) = -e^{-x} + (x - 4) e^{-x} = (x - 5) e^{-x}$$
**For $f_3(x) = \frac{\ln(x^2 + 1)}{x^2 + 1}$:**
- Let $u = \ln(x^2 + 1)$, $v = x^2 + 1$
- $u' = \frac{2x}{x^2 + 1}$
- $v' = 2x$
- Using quotient rule:
$$f_3'(x) = \frac{u'v - uv'}{v^2} = \frac{\frac{2x}{x^2 + 1} (x^2 + 1) - \ln(x^2 + 1) (2x)}{(x^2 + 1)^2} = \frac{2x - 2x \ln(x^2 + 1)}{(x^2 + 1)^2} = \frac{2x (1 - \ln(x^2 + 1))}{(x^2 + 1)^2}$$
**For $f_4(x) = -x + 7 + 6 \ln(2x + 1) - 6 \ln(2x + 2)$:**
- Derivative of $-x$ is $-1$
- Derivative of constant $7$ is $0$
- Derivative of $6 \ln(2x + 1)$ is $6 \cdot \frac{2}{2x + 1} = \frac{12}{2x + 1}$
- Derivative of $-6 \ln(2x + 2)$ is $-6 \cdot \frac{2}{2x + 2} = -\frac{12}{2x + 2}$
- Summing up:
$$f_4'(x) = -1 + \frac{12}{2x + 1} - \frac{12}{2x + 2}$$
**For $f_5(x) = \frac{5^x}{5^{2x - 1}}$:**
- Simplify first:
$$f_5(x) = 5^{x - (2x - 1)} = 5^{x - 2x + 1} = 5^{1 - x}$$
- Derivative:
$$f_5'(x) = 5^{1 - x} \cdot \ln(5) \cdot (-1) = - \ln(5) \cdot 5^{1 - x}$$
4. **Final answers:**
$$f_1'(x) = 2 \sqrt{-3x + 2} - \frac{3x}{\sqrt{-3x + 2}}$$
$$f_2'(x) = (x - 5) e^{-x}$$
$$f_3'(x) = \frac{2x (1 - \ln(x^2 + 1))}{(x^2 + 1)^2}$$
$$f_4'(x) = -1 + \frac{12}{2x + 1} - \frac{12}{2x + 2}$$
$$f_5'(x) = - \ln(5) \cdot 5^{1 - x}$$