Derivative Questions
1. Problem: Find the value of $f'(3)$ for $f(x)=x^5+6x+4$.
2. Differentiate $f(x)$:
$$f'(x)=5x^4+6$$
3. Evaluate at $x=3$:
$$f'(3)=5(3)^4+6=5(81)+6=405+6=411$$
Answer: 411 (option d).
4. Problem: Is the statement "A function is increasing on an interval if its derivative is negative on that interval" true?
5. Explanation: A function is increasing if its derivative is positive, not negative.
Answer: False (option a).
6. Problem: If $f'(x) > 0$ at a critical point, does the function have a relative maximum there?
7. Explanation: At a critical point, if $f'(x) > 0$, the function is increasing, so it cannot be a relative maximum.
Answer: False (option b).
8. Problem: Which statement is true if $f'(x) > 0$ for all $x$ in interval $I$?
9. Explanation: Positive derivative means function is increasing.
Answer: $f(x)$ is increasing on $I$ (option d).
10. Problem: Find the equation of the tangent line to $f(x)=x^3-2x$ at $(1,-1)$.
11. Differentiate:
$$f'(x)=3x^2-2$$
12. Evaluate slope at $x=1$:
$$f'(1)=3(1)^2-2=3-2=1$$
13. Use point-slope form:
$$y - (-1) = 1(x - 1) \\ y + 1 = x - 1 \\ y = x - 2$$
Answer: $y=x-2$ (option b).
14. Problem: Is a monotonic function both increasing and decreasing?
15. Explanation: Monotonic means either entirely non-increasing or non-decreasing, not both.
Answer: False (option b).
16. Problem: Is a point where $f'(x)=0$ and changes sign called a relative extremum?
17. Explanation: Yes, such points are relative maxima or minima.
Answer: True (option a).
18. Problem: Find the point of tangency where slope of tangent to $y=x^2-4x+5$ at $x=2$ is zero.
19. Differentiate:
$$y' = 2x - 4$$
20. Evaluate slope at $x=2$:
$$y'(2) = 2(2) - 4 = 4 - 4 = 0$$
21. Find $y$ at $x=2$:
$$y(2) = 2^2 - 4(2) + 5 = 4 - 8 + 5 = 1$$
Answer: $(2,1)$ (option d).
22. Problem: Find $f'(x)$ for $f(x)=x^6 - 2x^5 + 3x^2 - 23$.
23. Differentiate term-wise:
$$f'(x) = 6x^5 - 10x^4 + 6x$$
Answer: $6x^5 - 10x^4 + 6x$ (option d).
24. Problem: Find the derivative of $f(x) = x^5$.
25. Derivative:
$$f'(x) = 5x^4$$
Answer: $5x^4$ (option a).