Extreme Values
1. **Problem Statement:** Find the extreme values (absolute and local) of the function $y=2x^2 - 8x + 9$ over its natural domain.
2. **Formula and Rules:** To find extreme values, we first find the critical points by setting the derivative equal to zero: $$y' = \frac{dy}{dx}$$.
3. **Calculate the derivative:** $$y' = \frac{d}{dx}(2x^2 - 8x + 9) = 4x - 8$$.
4. **Find critical points:** Set derivative equal to zero:
$$4x - 8 = 0 \implies 4x = 8 \implies x = 2$$.
5. **Determine the nature of critical points:** Use the second derivative test:
$$y'' = \frac{d}{dx}(4x - 8) = 4$$.
Since $y'' = 4 > 0$, the function is concave up at $x=2$, so this point is a local minimum.
6. **Find the value of $y$ at $x=2$:**
$$y(2) = 2(2)^2 - 8(2) + 9 = 8 - 16 + 9 = 1$$.
7. **Check endpoints and domain:** The domain is all real numbers, so no endpoints.
8. **Conclusion:** The function has a local (and absolute) minimum at $x=2$ with value $y=1$. There is no maximum since the parabola opens upward.
**Final answer:** Local and absolute minimum at $(2,1)$.
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Repeat similar steps for each function:
**54.** $y = x^3 - 2x + 4$
- Derivative: $y' = 3x^2 - 2$
- Critical points: $3x^2 - 2 = 0 \implies x = \pm \sqrt{\frac{2}{3}}$
- Second derivative: $y'' = 6x$
- At $x=\sqrt{2/3}$, $y'' > 0$ local min; at $x=-\sqrt{2/3}$, $y'' < 0$ local max.
**55.** $y = x^3 + x^2 - 8x + 5$
- Derivative: $y' = 3x^2 + 2x - 8$
- Solve $3x^2 + 2x - 8=0$ for critical points.
- Second derivative: $y'' = 6x + 2$
**56.** $y = x^3(x-5)^2$
- Expand or use product rule to find $y'$.
- Find critical points by solving $y' = 0$.
**57.** $y = \sqrt{x^2 - 1}$
- Domain: $|x| \geq 1$
- Derivative: $y' = \frac{x}{\sqrt{x^2 - 1}}$
- Critical points where numerator zero or derivative undefined.
**58.** $y = x - 4\sqrt{x}$
- Domain: $x \geq 0$
- Derivative: $y' = 1 - \frac{2}{\sqrt{x}}$
- Solve $y' = 0$ for critical points.
**59.** $y = \frac{1}{\sqrt{1 - x^2}}$
- Domain: $|x| < 1$
- Derivative: Use chain and quotient rules.
**60.** $y = \sqrt{3} + 2x - x^2$
- Derivative: $y' = 2 - 2x$
- Critical point at $x=1$.
**61.** $y = \frac{x}{x^2 + 1}$
- Derivative: Use quotient rule.
**62.** $y = \frac{x+1}{x^2 + 2x + 2}$
- Derivative: Use quotient rule.
**63.** $y = e^x + e^{-x}$
- Derivative: $y' = e^x - e^{-x}$
- Critical point at $x=0$.
**64.** $y = e^x - e^{-x}$
- Derivative: $y' = e^x + e^{-x} > 0$ always, no critical points.
**65.** $y = x \ln x$
- Domain: $x > 0$
- Derivative: $y' = \ln x + 1$
- Critical point at $x = e^{-1}$.
**66.** $y = x^2 \ln x$
- Domain: $x > 0$
- Derivative: $y' = 2x \ln x + x$
- Solve $y' = 0$.
**67.** $y = \cos^{-1}(x^2)$
- Domain: $|x| \leq 1$
- Derivative: $y' = \frac{-2x}{\sqrt{1 - x^4}}$
**68.** $y = \sin^{-1}(e^x)$
- Domain: $e^x \in [-1,1] \implies x \leq 0$
- Derivative: $y' = \frac{e^x}{\sqrt{1 - e^{2x}}}$
**Summary:** Each function's critical points are found by setting $y' = 0$ and analyzing $y''$ or using first derivative test to classify extrema. Absolute extrema depend on domain boundaries.