Chapter 3: Problem 67
For each polynomial, at least one zero is given. Find all others analytically. $$P(x)=x^{4}-41 x^{2}+180 ; \quad-6 \text { and } 6$$
Short Answer
Expert verified
The zeros of the polynomial are \(-6, 6, \sqrt{5}, -\sqrt{5}\).
Step by step solution
01
Identify the Given Zeros
You are given that the polynomial function is \(P(x) = x^4 - 41x^2 + 180\) and that \(x = -6\) and \(x = 6\) are zeros of the polynomial. This means \(P(-6) = 0\) and \(P(6) = 0\). Since the polynomial is an even function (the powers of \(x\) are even), it is symmetric. The polynomial must also be divisible by both \((x + 6)\) and \((x - 6)\).
02
Use Factoring Approach
Since \(x = -6\) and \(x = 6\) are zeros, a factor of \(P(x)\) is \((x^2 - 36)\), because \((x - 6)(x + 6) = x^2 - 36\). Divide the polynomial by this factor to find the remaining factors. Perform the division:\[\frac{x^4 - 41x^2 + 180}{x^2 - 36}\].
03
Perform Polynomial Division
Divide \(x^4 - 41x^2 + 180\) by \(x^2 - 36\) using polynomial long division. Start by dividing \(x^4\) by \(x^2\) to get \(x^2\). Multiply \(x^2\) with \(x^2 - 36\) to get \(x^4 - 36x^2\). Subtract from the original polynomial to get \(-5x^2 + 180\).
04
Complete the Division
Continue the division by dividing \(-5x^2\) by \(x^2\) to get \(-5\). Multiply \(-5\) by \(x^2 - 36\) to get \(-5x^2 + 180\). Subtract this from \(-5x^2 + 180\) to get a remainder of 0, indicating \(P(x) = (x^2 - 36)(x^2 - 5)\).
05
Solve for Remaining Zeros
Now solve \(x^2 - 5 = 0\) to find the remaining zeros. Rewrite as \(x^2 = 5\), then take the square root of both sides to get \(x = \sqrt{5}\) and \(x = -\sqrt{5}\). Therefore, the zeros of the polynomial are \(x = -6, 6, \sqrt{5}, -\sqrt{5}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Division
Polynomial Division is a technique used to divide one polynomial by another, often resulting in a quotient and a remainder. In this exercise, we are dividing the polynomial \(P(x) = x^4 - 41x^2 + 180\) by the factor \(x^2 - 36\). Start by aligning the terms of \(x^4 - 41x^2 + 180\) with \(x^2 - 36\).
- First, divide the leading term \(x^4\) by \(x^2\), resulting in \(x^2\).
- Next, multiply \(x^2\) by the divisor \(x^2 - 36\), which gives \(x^4 - 36x^2\).
- Subtract this from the original polynomial to simplify.
- This process continues until the entire polynomial is divided, ensuring the remainder is zero when perfectly divisible.
Factoring Polynomials
Factoring Polynomials is the process of breaking down a polynomial into simpler components or factors that, when multiplied together, rapidly form the original polynomial.In the exercise, once we identified the zeros, \(x = -6\) and \(x = 6\), we found a common factor: \((x + 6)(x - 6) = x^2 - 36\). This illustrates the symmetry in polynomials, particularly when dealing with even functions. After discovering \(x^2 - 36\) as a factor, we performed polynomial division on \(P(x)\) to further factor it as \((x^2 - 36)(x^2 - 5)\).
- Recognizing patterns, like squares and differences of squares, can simplify factorizations.
- Using given zeros to create factors often leads to uncovering additional zeros.
Roots of Polynomials
Roots or zeros of a polynomial are the values of \(x\) that make the polynomial equal to zero. In essence, they are where the polynomial crosses the x-axis. Finding these roots involves several techniques, including substitution, factorizing, and using the quadratic formula.For the given polynomial \(P(x) = x^4 - 41x^2 + 180\), we were initially provided with two zeros: \(x = -6\) and \(x = 6\). By factoring, we found additional zeros from \(x^2 - 5 = 0\), calculated as \(x = \sqrt{5}\) and \(x = -\sqrt{5}\).
- Zeros are critical as they reveal the solutions to the polynomial equation.
- They help in sketching the graph of the polynomial, demonstrating its behavior across different intervals.
- Understanding the relationship between roots and factors expedites the solving of complex polynomials.