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a polynomial function has x-intercepts at -2, \\(\\frac{1}{2}\\), and 2…

Question

a polynomial function has x-intercepts at -2, \\(\frac{1}{2}\\), and 2 and a relative maximum at x = -1. which graph matches the description of this function? \\(\circ\\) a. graph a \\(\circ\\) b. graph b \\(\circ\\) c. graph c (partially shown)

Explanation:

Step1: Check x-intercepts

The polynomial has x-intercepts at \(-2\), \(\frac{1}{2}\), and \(2\). So the graph should cross the x-axis at these points. Let's check the options:

  • Option A: Crosses at \(-2\), \(\frac{1}{2}\) (between \(0\) and \(1\)), and \(2\).
  • Option B: Crosses at \(-2\), some point between \(-1\) and \(0\) (not \(\frac{1}{2}\)), and \(2\). So B fails here.

Step2: Check relative maximum at \(x = -1\)

A relative maximum at \(x=-1\) means the graph has a peak (highest point in a local region) at \(x=-1\).

  • Option A: At \(x=-1\), the graph has a minimum (lowest point in local region), which is a relative minimum, not maximum. Wait, no—wait, let's re-examine. Wait, in Option A, the left part: from left, comes down, crosses \(-2\), then has a minimum around \(x=-1\)? Wait no, maybe I mixed up. Wait Option B: at \(x=-1\), the graph has a peak (relative maximum). Wait, let's re-express.

Wait, the x-intercepts: \(-2\), \(1/2\), \(2\). So the roots are \(x=-2\), \(x = 1/2\), \(x=2\). So the polynomial is of the form \(y = a(x + 2)(x - 1/2)(x - 2)\). Now, the end behavior: if the leading coefficient \(a\) is positive, as \(x\to\infty\), \(y\to\infty\); as \(x\to-\infty\), \(y\to-\infty\). If \(a\) is negative, opposite.

Now, relative maximum at \(x=-1\): the derivative at \(x=-1\) is zero, and the function changes from increasing to decreasing there.

Looking at Option B: the graph comes from below, rises, has a peak at \(x=-1\) (relative maximum), then falls, crosses \(x=0\) (but wait, the root is \(x=1/2\), so between \(0\) and \(1\)), then has a minimum, then rises through \(x=2\). Wait, but the x-intercept at \(1/2\): in Option B, the graph crosses the x-axis between \(-1\) and \(0\)? No, \(1/2\) is between \(0\) and \(1\). So Option A crosses at \(x=1/2\) (between \(0\) and \(1\)), Option B crosses between \(-1\) and \(0\), which is not \(1/2\). So Option A has x-intercepts at \(-2\), \(1/2\) (between \(0\) and \(1\)), and \(2\). Then, relative maximum: wait, maybe I made a mistake earlier. Wait, in Option B, the relative maximum is at \(x=-1\), but the x-intercept at \(1/2\) is wrong. In Option A, the relative minimum is at \(x=-1\)? Wait no, let's look again.

Wait the problem says "a relative maximum at \(x = -1\)". So the graph should have a peak (highest point) at \(x=-1\). Let's check the two options:

Option A: The graph, when moving from left to right: starts from top left, comes down, crosses \(x=-2\), then goes to a minimum (low point) around \(x=-1\) (relative minimum), then rises, crosses \(x=1/2\) (between \(0\) and \(1\)), then rises to a maximum around \(x=1\), then falls through \(x=2\). So relative maximum at \(x=1\), not \(x=-1\).

Option B: The graph starts from bottom left, rises, has a peak (relative maximum) at \(x=-1\), then falls, crosses the x-axis between \(-1\) and \(0\) (but that should be \(x=1/2\), which is between \(0\) and \(1\)), then falls to a minimum, then rises through \(x=2\). Wait, but the x-intercept at \(1/2\) is not correct in B. Wait, maybe the original problem's Option A and B: let's re-express.

Wait, maybe I messed up the x-intercept at \(1/2\). Let's check the graphs again. In Option A, the graph crosses the x-axis at \(x=-2\), \(x\) between \(0\) and \(1\) (which is \(1/2\)), and \(x=2\). In Option B, the graph crosses at \(x=-2\), \(x\) between \(-1\) and \(0\) (not \(1/2\)), and \(x=2\). So Option A has the correct x-intercepts. Now, relative maximum at \(x=-1\): wait, maybe the problem has a typo, or I misread. Wait the problem says "a relative maximum at \(x…

Answer:

Step1: Check x-intercepts

The polynomial has x-intercepts at \(-2\), \(\frac{1}{2}\), and \(2\). So the graph should cross the x-axis at these points. Let's check the options:

  • Option A: Crosses at \(-2\), \(\frac{1}{2}\) (between \(0\) and \(1\)), and \(2\).
  • Option B: Crosses at \(-2\), some point between \(-1\) and \(0\) (not \(\frac{1}{2}\)), and \(2\). So B fails here.

Step2: Check relative maximum at \(x = -1\)

A relative maximum at \(x=-1\) means the graph has a peak (highest point in a local region) at \(x=-1\).

  • Option A: At \(x=-1\), the graph has a minimum (lowest point in local region), which is a relative minimum, not maximum. Wait, no—wait, let's re-examine. Wait, in Option A, the left part: from left, comes down, crosses \(-2\), then has a minimum around \(x=-1\)? Wait no, maybe I mixed up. Wait Option B: at \(x=-1\), the graph has a peak (relative maximum). Wait, let's re-express.

Wait, the x-intercepts: \(-2\), \(1/2\), \(2\). So the roots are \(x=-2\), \(x = 1/2\), \(x=2\). So the polynomial is of the form \(y = a(x + 2)(x - 1/2)(x - 2)\). Now, the end behavior: if the leading coefficient \(a\) is positive, as \(x\to\infty\), \(y\to\infty\); as \(x\to-\infty\), \(y\to-\infty\). If \(a\) is negative, opposite.

Now, relative maximum at \(x=-1\): the derivative at \(x=-1\) is zero, and the function changes from increasing to decreasing there.

Looking at Option B: the graph comes from below, rises, has a peak at \(x=-1\) (relative maximum), then falls, crosses \(x=0\) (but wait, the root is \(x=1/2\), so between \(0\) and \(1\)), then has a minimum, then rises through \(x=2\). Wait, but the x-intercept at \(1/2\): in Option B, the graph crosses the x-axis between \(-1\) and \(0\)? No, \(1/2\) is between \(0\) and \(1\). So Option A crosses at \(x=1/2\) (between \(0\) and \(1\)), Option B crosses between \(-1\) and \(0\), which is not \(1/2\). So Option A has x-intercepts at \(-2\), \(1/2\) (between \(0\) and \(1\)), and \(2\). Then, relative maximum: wait, maybe I made a mistake earlier. Wait, in Option B, the relative maximum is at \(x=-1\), but the x-intercept at \(1/2\) is wrong. In Option A, the relative minimum is at \(x=-1\)? Wait no, let's look again.

Wait the problem says "a relative maximum at \(x = -1\)". So the graph should have a peak (highest point) at \(x=-1\). Let's check the two options:

Option A: The graph, when moving from left to right: starts from top left, comes down, crosses \(x=-2\), then goes to a minimum (low point) around \(x=-1\) (relative minimum), then rises, crosses \(x=1/2\) (between \(0\) and \(1\)), then rises to a maximum around \(x=1\), then falls through \(x=2\). So relative maximum at \(x=1\), not \(x=-1\).

Option B: The graph starts from bottom left, rises, has a peak (relative maximum) at \(x=-1\), then falls, crosses the x-axis between \(-1\) and \(0\) (but that should be \(x=1/2\), which is between \(0\) and \(1\)), then falls to a minimum, then rises through \(x=2\). Wait, but the x-intercept at \(1/2\) is not correct in B. Wait, maybe the original problem's Option A and B: let's re-express.

Wait, maybe I messed up the x-intercept at \(1/2\). Let's check the graphs again. In Option A, the graph crosses the x-axis at \(x=-2\), \(x\) between \(0\) and \(1\) (which is \(1/2\)), and \(x=2\). In Option B, the graph crosses at \(x=-2\), \(x\) between \(-1\) and \(0\) (not \(1/2\)), and \(x=2\). So Option A has the correct x-intercepts. Now, relative maximum at \(x=-1\): wait, maybe the problem has a typo, or I misread. Wait the problem says "a relative maximum at \(x = -1\)". But in Option A, at \(x=-1\), it's a minimum. In Option B, at \(x=-1\), it's a maximum. But Option B has wrong x-intercept at \(1/2\). Wait, this is confusing. Wait, maybe the polynomial is of odd degree (three roots, so degree 3). For a cubic polynomial, the number of turning points is at most 2. So it can have a relative maximum and a relative minimum.

Wait, let's calculate the derivative. Let \(f(x) = a(x + 2)(x - 1/2)(x - 2)\). Expand: \(f(x) = a(x + 2)(x - 2)(x - 1/2) = a(x^2 - 4)(x - 1/2) = a(x^3 - (1/2)x^2 - 4x + 2)\). Then \(f'(x) = a(3x^2 - x - 4)\). Set \(f'(x) = 0\): \(3x^2 - x - 4 = 0\). Solve: \(x = \frac{1 \pm \sqrt{1 + 48}}{6} = \frac{1 \pm 7}{6}\). So \(x = \frac{8}{6} = \frac{4}{3}\) or \(x = \frac{-6}{6} = -1\). Ah! So the critical points are at \(x=-1\) and \(x = 4/3\). So the relative maximum is at \(x=-1\) (since for cubic, if leading coefficient \(a > 0\), the left critical point is a maximum, right is a minimum). So \(f'(x) = a(3x^2 - x - 4)\). If \(a > 0\), then at \(x=-1\), the function changes from increasing to decreasing (relative maximum), and at \(x=4/3\), changes from decreasing to increasing (relative minimum).

Now, let's check the end behavior: as \(x\to\infty\), \(f(x)\to\infty\) (since \(a > 0\) and degree 3), and as \(x\to-\infty\), \(f(x)\to-\infty\). So the graph should come from below (as \(x\to-\infty\)), rise, have a maximum at \(x=-1\), then fall, have a minimum at \(x=4/3\), then rise to \(\infty\) as \(x\to\infty\).

Now, check the options:

Option B: comes from below (left end), rises, has a maximum at \(x=-1\) (correct), then falls, crosses the x-axis at \(x=1/2\) (wait, no, in Option B, the graph crosses the x-axis between \(-1\) and \(0\), which is not \(1/2\)). Wait, no—wait \(1/2\) is between \(0\) and \(1\). So Option A: comes from above (left end), falls, crosses \(x=-2\), then falls to a minimum at \(x=-1\) (but that's a minimum, not maximum), then rises, crosses \(x=1/2\) (between \(0\) and \(1\)), then rises to a maximum at \(x=4/3\) (around \(x=1\)), then falls to \(-\infty\) as \(x\to\infty\). But that's end behavior \(x\to\infty\) goes to \(-\infty\), which would mean \(a < 0\).

Wait, if \(a < 0\), then end behavior: \(x\to\infty\), \(f(x)\to-\infty\); \(x\to-\infty\), \(f(x)\to\infty\). Then the critical points: at \(x=-1\), since \(a < 0\), the derivative \(f'(x) = a(3x^2 - x - 4)\). At \(x=-1\), \(3(-1)^2 - (-1) - 4 = 3 + 1 - 4 = 0\). The second derivative or sign change: for \(a < 0\), when \(x < -1\), \(3x^2 - x - 4\): at \(x=-2\), \(3(4) - (-2) - 4 = 12 + 2 - 4 = 10 > 0\), so \(f'(x) = a(positive) < 0\) (since \(a < 0\)), so function is decreasing before \(x=-1\). At \(x=0\), \(3(0) - 0 - 4 = -4 < 0\), so \(f'(x) = a(negative) > 0\) (since \(a < 0\)), so function is increasing after \(x=-1\). Wait, that would mean at \(x=-1\), the function changes from decreasing to increasing, so it's a relative minimum, not maximum. Contradiction. So maybe \(a > 0\), end behavior \(x\to\infty\) \(f(x)\to\infty\), \(x\to-\infty\) \(f(x)\to-\infty\). Then, before \(x=-1\), \(f'(x) = a(positive) > 0\) (since \(x < -1\), \(3x^2 - x - 4 > 0\)), so function is increasing. After \(x=-1\), \(x\) between \(-1\) and \(4/3\), \(3x^2 - x - 4 < 0\) (at \(x=0\), it's \(-4\)), so \(f'(x) = a(negative) < 0\), so function is decreasing. So at \(x=-1\), the function changes from increasing to decreasing, so it's a relative maximum (correct). Then, after \(x=4/3\), \(3x^2 - x - 4 > 0\) (at \(x=2\), \(3(4) - 2 - 4 = 12 - 6 = 6 > 0\)), so \(f'(x) = a(positive) > 0\), function is increasing.

So the graph should: come from below (as \(x\to-\infty\)), rise, have a maximum at \(x=-1\), then fall, have a minimum at \(x=4/3\), then rise to \(\infty\) as \(x\to\infty\). Now, check the x-intercepts: \(x=-2\), \(x=1/2\), \(x=2\).

Option B: comes from below (left end), rises, has a maximum at \(x=-1\) (correct), then falls, crosses \(x=1/2\) (between \(0\) and \(1\))? Wait, in Option B, the graph crosses the x-axis between \(-1\) and \(0\), which is not \(1/2\). Option A: comes from above (left end), falls, crosses \(x=-2\), then falls to a minimum at \(x=-1\) (which would be a relative minimum, not maximum), then rises, crosses \(x=1/2\) (between \(0\) and \(1\)), then rises to a maximum at \(x=4/3\), then falls to \(-\infty\) (end behavior \(x\to\infty\) \(f(x)\to-\infty\)), which would mean \(a < 0\). But then the relative maximum at \(x=-1\) is not there. Wait, I think I made a mistake in the initial x-intercept check. Wait the problem says x-intercepts at \(-2\), \(1/2\), and \(2\). So the graph must cross the x-axis at these three points. Option A crosses at \(-2\), \(1/2\) (between \(0\) and \(1\)), and \(2\). Option B crosses at \(-2\), a point between \(-1\) and \(0\) (not \(1/2\)), and \(2\). So Option B fails the x-intercept at \(1/2\). Therefore, the correct graph must be Option B? Wait no, wait \(1/2\) is 0.5, between 0 and 1. In Option A, the graph crosses the x-axis between 0 and 1 (at \(x=1/2\)), and in Option B, it crosses between -1 and 0 (which is not 0.5). So Option A has the correct x-intercepts. But then the relative maximum at \(x=-1\): in Option A, at \(x=-1\), the graph is at a minimum (the lowest point in that local area), which is a relative minimum. But the problem says relative maximum at \(x=-1\). So there's a contradiction unless I misread the options. Wait, maybe the original problem's Option B has the x-intercept at \(1/2\). Wait, looking at the graph for Option B: the graph crosses the x-axis between -1 and 0? No, maybe the grid is such that the x-intercept is at \(1/2\). Wait, maybe the user's image for Option B has the x-intercept at \(1/2\). Alternatively, maybe I mixed up the relative maximum and minimum. Wait, the critical points are at \(x=-1\) (maximum) and \(x=4/3\) (minimum) when \(a > 0\). So the graph should rise to \(x=-1\) (maximum), then fall to \(x=4/3\) (minimum), then rise. So the left end: as \(x\to-\infty\), \(f(x)\to-\infty\) (since \(a > 0\), degree 3), so the graph comes from below, rises, peaks at \(x=-1\), then falls, crosses \(x=1/2\), then falls to a minimum at \(x=4/3\), then rises to \(\infty\) as \(x\to\infty\). So the graph should have:

  • Left end: coming from below (\(x\to-\infty\), \(y\to-\infty\))
  • Rises to a maximum at \(x=-1\)
  • Falls, crosses \(x=-2\)? No, wait \(x=-2\) is a root, so it should cross \(x=-2\) on the way up. Wait, no: the roots are \(x=-2\), \(x=1/2\), \(x=2\). So the graph crosses \(x=-2\) (from below to above, since it's a single root, not a double root), then rises to \(x=-1\) (maximum), then falls, crosses \(x=1/2\) (from above to below), then falls to \(x=4/3\) (minimum), then rises, crosses \(x=2\) (from below to above), then goes to \(\infty\). Wait, that would mean the graph crosses \(x=-2\) (from negative to positive), then rises to \(x=-1\) (maximum), then falls, crosses \(x=1/2\) (positive to negative), then falls to minimum at \(x=4/3\), then rises, crosses \(x=2\) (negative to positive), then to \(\infty\). So the y-intercept: when \(x=0\), \(y = a(0 + 2)(0 - 1/2)(0 - 2) = a(2)(-1/2)(-2) = a(2)\). So if \(a > 0\), y-intercept is positive. If \(a < 0\), y-intercept is negative.

Looking at Option A: y-intercept is negative (crosses y-axis below zero). Option B: y-intercept is negative? Wait, in Option A, the graph at \(x=0\) is below zero (y-intercept negative). In Option B, at \(x=0\), the graph is below zero. Wait, maybe \(a < 0\). Then, end behavior: \(x\to\infty\), \(f(x)\to-\infty\); \(x\to-\infty\), \(f(x)\to\infty\). So the graph comes from above, falls, crosses \(x=-2\) (positive to negative), then falls to a minimum at \(x=-1\) (relative minimum), then rises, crosses \(x=1/2\) (negative to positive), then rises to a maximum at \(x=4/3\) (relative maximum), then falls to \(-\infty\) as \(x\to\infty\). But the problem says relative maximum at \(x=-1\), which would not be the