Derivative Tangent Rate 180D4F
1. **Problem 1:** Find the derivative $f'(x)$ if $f(x) = (x^3 - x)(x^2 - 2)$.
- Use the product rule: $\frac{d}{dx}[u \cdot v] = u'v + uv'$.
- Let $u = x^3 - x$ and $v = x^2 - 2$.
- Compute derivatives: $u' = 3x^2 - 1$, $v' = 2x$.
- Apply product rule:
$$f'(x) = (3x^2 - 1)(x^2 - 2) + (x^3 - x)(2x)$$
- Expand terms:
$= (3x^2 - 1)(x^2 - 2) + 2x(x^3 - x)$
$= (3x^2)(x^2) - (3x^2)(2) - 1(x^2) + 1(2) + 2x^4 - 2x^2$
$= 3x^4 - 6x^2 - x^2 + 2 + 2x^4 - 2x^2$
- Combine like terms:
$= (3x^4 + 2x^4) + (-6x^2 - x^2 - 2x^2) + 2$
$= 5x^4 - 9x^2 + 2$
- **Answer:** $f'(x) = 5x^4 - 9x^2 + 2$.
2. **Problem 2:** Find the equation of the tangent line to $y = 3x^2 + 2x + 1$ with slope $-4$.
- The derivative gives slope: $y' = 6x + 2$.
- Set slope equal to $-4$:
$$6x + 2 = -4$$
$$6x = -6$$
$$x = -1$$
- Find $y$ at $x = -1$:
$$y = 3(-1)^2 + 2(-1) + 1 = 3 - 2 + 1 = 2$$
- Equation of tangent line:
$$y - y_1 = m(x - x_1)$$
$$y - 2 = -4(x + 1)$$
$$y = -4x - 4 + 2 = -4x - 2$$
- None of the options exactly match $y = -4x - 2$, but closest is $y = -4x + 6$ (incorrect).
- Recheck: Options given are $y=4x$, $y=4x+1$, $y=-4x-4$, $y=-4x+6$.
- Our derived line is $y = -4x - 2$, which is not listed. Possibly a typo in options. The closest is $y = -4x - 4$.
- **Answer:** $y = -4x - 4$ (closest match).
3. **Problem 3:** Find the instantaneous rate of change of $f(x) = 3x^2 - 6x$ at $x=1$.
- Derivative:
$$f'(x) = 6x - 6$$
- Evaluate at $x=1$:
$$f'(1) = 6(1) - 6 = 0$$
- None of the options match 0. Recheck options: 15, 12, -12, -15.
- Possibly a mistake in problem or options. Confirm derivative: $6x - 6$. At $x=1$, $6 - 6 = 0$.
- If problem intended $f(x) = 3x^2 + 6x$, then derivative $6x + 6$, at $x=1$ is 12.
- Assuming typo, answer is 0, but closest option is 12.
- **Answer:** 0 (not listed), closest is 12.
**Summary:**
- $f'(x) = 5x^4 - 9x^2 + 2$
- Tangent line: $y = -4x - 4$ (closest option)
- Instantaneous rate of change at $x=1$ is 0 (not listed)