Chapter 5: Problem 162
Factor each polynomial using the trial-and-error method. $$ 3 x^{2}-25 x+8 $$
Short Answer
Expert verified
(3x - 1)(x - 8)
Step by step solution
01
Identify the coefficients
The coefficients of the quadratic polynomial are: a = 3, b = -25, and c = 8.
02
Set up the factored form
The factored form of a quadratic polynomial is \[ (mx + n)(px + q) \]. Based on the coefficient a=3, we can assume m and p to be factors of 3, which are 3 and 1. So, we guess the factors as \[ (3x + n)(x + q) \].
03
Find pairs of factors for ac
The product of a and c is 3 * 8 = 24. Find pairs of factors of 24 that add up to the middle coefficient b, which is -25. The pairs are: (-1, -24), (1, 24), (2, 12), (3, 8), (-3, -8), etc.
04
Select the appropriate factor pairs
Among the factor pairs, we find that -1 and -24 add up to -25: \[-1 + (-24) = -25\]
05
Substitute and solve
Write the polynomial as \[ 3x^2 - x - 24x + 8\] and group terms to factor by grouping: \[ x(3x - 1) - 8(3x - 1) = (3x - 1)(x - 8)\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic polynomial
A quadratic polynomial is a type of polynomial that features a term raised to the second power. Generally, it can be written in the form: \[ ax^2 + bx + c \] where `a`, `b`, and `c` are coefficients and `a` is not equal to zero. In the context of our example, the quadratic polynomial is \[ 3x^2 - 25x + 8 \] This equation represents a parabola when graphed. The quadratic term (\(3x^2\)) is what gives the parabola its characteristic ‘U’ shape.
- The coefficient `a` (3) affects the width and direction of the parabola.
- The coefficient `b` (-25) affects the location of the vertex and the axis of symmetry.
- The constant `c` (8) determines the y-intercept of the graph.
trial-and-error method
The trial-and-error method is a systematic way to factor quadratic polynomials. Instead of relying solely on formulas, this method involves testing potential factor pairs until the correct ones are found. To factor \[ 3x^2 - 25x + 8 \] we follow these steps:
- Identify the coefficients: `a` (3), `b` (-25), and `c` (8).
- Set up the factored form: \[ (mx + n)(px + q) \] Since `a` is 3, we use factor pairs of 3: (3, 1).
- Find pairs of factors for the product of `a` and `c` (3 * 8 = 24).
- Check factor pairs that add up to -25: (-1, -24).
- Rewrite and factor by grouping: \[ 3x^2 - x - 24x + 8 \rightarrow x(3x - 1) - 8(3x - 1) \rightarrow (3x - 1)(x - 8) \]
factor pairs
In the process of factoring quadratic polynomials, identifying factor pairs is crucial. Factor pairs are sets of two numbers that, when multiplied together, give the product of `a` and `c` in the quadratic polynomial. For example, in \[ 3x^2 - 25x + 8 \] the product of coefficients `a` and `c` is 24 (3 * 8). The possible factor pairs of 24 include:
- (1, 24)
- (2, 12)
- (3, 8)
- (4, 6)
- (-1, -24)
- (-2, -12)
- (-3, -8)
- (-4, -6)