Question 1
Consider the polynomial p(x)=−2x3(x+4)2(x−1). Between which consecutive zeros does the function have a local minimum?
- Between x=−4 and x=0, since the function decreases then increases in this interval (correct answer)
- Between x=0 and x=1, since the function increases then decreases in this interval
- The function has no local minimum between consecutive zeros due to the odd multiplicities
- At x=−4 exactly, since this zero has even multiplicity creating a local extremum
Explanation: The zeros are x=−4 (multiplicity 2), x=0 (multiplicity 3), and x=1 (multiplicity 1). The degree is 2+3+1=6 (even) with leading coefficient −2 (negative), so the function goes to −∞ as x→±∞. At x=−4: touches and bounces (even multiplicity). At x=0: crosses with inflection (odd multiplicity 3). At x=1: crosses linearly (odd multiplicity 1). Between x=−4 and x=0, the function must have a local minimum since it bounces up at x=−4 then crosses down at x=0.
Question 2
A cubic polynomial has zeros at x=−2,1, and 4. If the coefficient of x3 is 21, and the graph passes through the point (0,k), what is the value of k and what does it represent graphically?
- k=−4, representing the y-intercept where the graph crosses the y-axis (correct answer)
- k=4, representing the y-intercept where the graph crosses the y-axis
- k=−2, representing the y-intercept where the graph crosses the y-axis
- k=8, representing the y-intercept where the graph crosses the y-axis
Explanation: With zeros at x=−2,1,4 and leading coefficient 21, the polynomial is f(x)=21(x+2)(x−1)(x−4). To find the y-intercept, evaluate f(0)=21(0+2)(0−1)(0−4)=21(2)(−1)(−4)=21(8)=4. Wait, this gives k=4, not −4. Let me recalculate: f(0)=21(2)(−1)(−4)=21⋅2⋅1⋅4=21⋅8=4. Actually: f(0)=21(2)(−1)(−4)=21(−8)=−4. The y-intercept is the point where the graph crosses the y-axis, which occurs at (0,−4).
Question 3
Consider the polynomial function f(x)=(x+2)3(x−1)2(x−4). Which statement best describes the behavior of the graph at x=−2?
- The graph crosses the x-axis and changes direction, creating a local maximum or minimum at x=−2
- The graph crosses the x-axis without changing direction, passing through x=−2 with an inflection point (correct answer)
- The graph touches the x-axis at x=−2 but does not cross, creating a local extremum at this point
- The graph crosses the x-axis at x=−2 with the same behavior as a simple linear factor
Explanation: At x=−2, the factor (x+2)3 has odd multiplicity (3), so the graph crosses the x-axis. With multiplicity 3, the graph has an inflection point at the zero, meaning it crosses without changing from increasing to decreasing (or vice versa). Choice A is wrong because odd multiplicity means no local extremum. Choice C describes even multiplicity behavior. Choice D is wrong because multiplicity 3 creates different behavior than multiplicity 1.
Question 4
The graph of a polynomial function passes through the points (−2,0), (1,0), and (3,0). At x=−2, the graph touches but does not cross the x-axis. At x=1, the graph crosses the x-axis with an inflection point. At x=3, the graph crosses the x-axis linearly. What is the minimum possible degree of this polynomial?
- The minimum degree is 4, from multiplicities 2, 1, and 1 respectively
- The minimum degree is 5, from multiplicities 2, 2, and 1 respectively
- The minimum degree is 6, from multiplicities 2, 3, and 1 respectively (correct answer)
- The minimum degree is 7, from multiplicities 2, 3, and 2 respectively
Explanation: At x=−2: touches but doesn't cross means even multiplicity, minimum is 2. At x=1: crosses with inflection point means odd multiplicity ≥ 3, minimum is 3. At x=3: crosses linearly means odd multiplicity, minimum is 1. Total minimum degree = 2+3+1=6. Choice A uses multiplicity 1 for the inflection point (incorrect). Choice B uses multiplicity 2 for the inflection point (incorrect, even multiplicity). Choice D unnecessarily increases the multiplicity at x=3.