Math Problem Statement

Determine the equation of the 5th degree polynomial that touches the x-axis at (-3,0), crosses the y-axis at (0,-4.5) and crosses the x-axis at (1,0)

Solution

To determine the equation of a 5th degree polynomial that meets the given conditions, we need to follow a systematic approach. Let's denote the polynomial by P(x)P(x).

Conditions given:

  1. The polynomial touches the x-axis at (3,0)(-3, 0). This means x=3x = -3 is a root with at least multiplicity 2.
  2. The polynomial crosses the y-axis at (0,4.5)(0, -4.5). This means P(0)=4.5P(0) = -4.5.
  3. The polynomial crosses the x-axis at (1,0)(1, 0). This means x=1x = 1 is a simple root.

Step-by-step solution:

  1. Identify the roots and their multiplicities:

    • Since the polynomial touches the x-axis at x=3x = -3, (3)(-3) must be a root with multiplicity at least 2.
    • Since the polynomial crosses the x-axis at x=1x = 1, 11 must be a simple root.

    Therefore, the polynomial can be written in the form: P(x)=a(x+3)2(x1)Q(x)P(x) = a(x + 3)^2(x - 1)Q(x) where Q(x)Q(x) is a polynomial of degree 2 because we need a polynomial of degree 5 in total.

  2. Determine Q(x)Q(x): Since we need a 5th degree polynomial and we already have 3 factors, Q(x)Q(x) must be a quadratic polynomial. Assume: Q(x)=(xr1)(xr2)Q(x) = (x - r_1)(x - r_2) where r1r_1 and r2r_2 are the remaining roots.

  3. Use the y-intercept condition: The polynomial crosses the y-axis at (0,4.5)(0, -4.5). Thus, P(0)=a(0+3)2(01)(0r1)(0r2)=4.5P(0) = a(0 + 3)^2(0 - 1)(0 - r_1)(0 - r_2) = -4.5 Simplifying, we get: 9a(1)(r1)(r2)=4.59a(-1)(-r_1)(-r_2) = -4.5 9ar1r2=4.59a r_1 r_2 = -4.5 ar1r2=4.59a r_1 r_2 = -\frac{4.5}{9} ar1r2=12a r_1 r_2 = -\frac{1}{2}

  4. Determine the unknowns: Since we need additional information to determine r1r_1 and r2r_2, let's proceed assuming specific roots to solve the problem, or express them symbolically.

    Suppose r1r_1 and r2r_2 are such that r1=rr_1 = r and r2=sr_2 = s. Then we have: P(x)=a(x+3)2(x1)(xr)(xs)P(x) = a(x + 3)^2(x - 1)(x - r)(x - s) with ars=12a \cdot r \cdot s = -\frac{1}{2}

  5. Solve for the roots rr and ss: Without additional constraints, assume simplest case:

    • Let r=2r = 2, then ss would be determined by: a2s=12a \cdot 2 \cdot s = -\frac{1}{2} as=14a \cdot s = -\frac{1}{4} If we assume a=1a = 1: s=14s = -\frac{1}{4}
  6. Construct the polynomial: P(x)=(x+3)2(x1)(x2)(x+14)P(x) = (x + 3)^2(x - 1)(x - 2)\left(x + \frac{1}{4}\right) If we include a constant aa to adjust for scaling: P(x)=a(x+3)2(x1)(x2)(4x+1)P(x) = a(x + 3)^2(x - 1)(x - 2)(4x + 1) Substitute P(0)=4.5P(0) = -4.5 to find aa: 4.5=a(3)2(1)(2)(1)4.5=a(9)(2)-4.5 = a(3)^2(-1)(-2)(1) \Rightarrow -4.5 = a(9)(2) 4.5=18aa=4.518=14-4.5 = 18a \Rightarrow a = -\frac{4.5}{18} = -\frac{1}{4}

  7. Final polynomial: P(x)=14(x+3)2(x1)(x2)(4x+1)P(x) = -\frac{1}{4} (x + 3)^2(x - 1)(x - 2)(4x + 1)

This is the polynomial of degree 5 that satisfies the given conditions.

Do you want more details or have any questions?

Relative questions:

  1. What is a polynomial's degree and why is it important?
  2. What is the difference between a root's multiplicity and a simple root?
  3. How do you determine a polynomial equation from its roots?
  4. How can you use the y-intercept to find a polynomial's leading coefficient?
  5. What are the implications of a polynomial touching the x-axis at a point?
  6. How can we verify that a given polynomial meets specific conditions?
  7. What role does the constant coefficient play in the polynomial equation?
  8. How do you graph a polynomial to visualize its roots and behavior?

Tip:

To understand the behavior of a polynomial function, always analyze its roots and their multiplicities, as well as how it intersects the axes.

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Math Problem Analysis

Mathematical Concepts

Polynomials
Roots and Multiplicities
Quadratic Equations
Y-intercept

Formulas

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Theorems

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Suitable Grade Level

Advanced High School / College