Problem 26 - College Algebra

Question

Factor each trinomial, or state that the trinomial is prime. $$ 3 x^{2}-2 x-5 $$

Step-by-Step Solution

Answer

The trinomial \(3x^2 - 2x - 5\) is prime.

Step 1: Identification

Identify the coefficients and constants in the trinomial. The coefficient of \(x^2\) is 3, the coefficient of \(x\) is -2, and the constant term is -5.

Step 2: Find the pair

Find two numbers that multiply to -15 and add up to -2, considering that these numbers may be either real numbers or irrational.

Step 3: Check for pair

Check for such pair. There is no pair of real or irrational numbers that satisfy these conditions hence the trinomial is prime.

Key Concepts

Polynomial Factoring

Factoring polynomials is a foundational skill in algebra. It involves expressing a polynomial as the product of simpler factors, much like breaking down a number into prime factors. For instance, the task often appears straightforward when dealing with a quadratic trinomial, which is generally in the form of \( ax^2 + bx + c \), where \( a \), \( b \), and \( c \) represent coefficients and constants.

In the case of factoring the trinomial \( 3x^2 - 2x - 5 \), you'd aim to rewrite this expression in the form \( (dx + e)(fx + g) \), where the product of \( d \) and \( f \) should give you \( a \), and the product of \( e \) and \( g \) should result in \( c \). Furthermore, the outer and inner products of the binomial terms \( (dx + e) \) and \( (fx + g) \) should sum to \( b \).

However, sometimes this process reveals that there are no such factors, which leads to the conclusion that the trinomial is prime and cannot be factored over the set of real or irrational numbers.

Trinomial Expressions

A trinomial expression is a type of polynomial with three terms. The structure of a quadratic trinomial is typically represented as \( ax^2 + bx + c \). To approach factoring, it's crucial to understand the role coefficients and constants play. In the example of \( 3x^2 - 2x - 5 \), '3' is the coefficient of the squared term, '-2' is the coefficient of the linear term, and '-5' is the constant term.

When attempting to factor trinomials, the search for two numbers that multiply to the product of \( a \) and \( c \), and add up to \( b \), is essentially a trial-and-error method grounded in algebraic understanding. In some cases, such as with the example provided, we conclude that there are no two numbers that meet these criteria, signifying that the trinomial is not factorable by regular algebraic methods.

Algebraic Techniques

Algebraic techniques for solving equations include a variety of methods, among which factoring stands out as a crucial strategy, especially when dealing with polynomial equations. The skillfulness in utilizing algebraic techniques can be likened to a craftsman's adeptness with their tools. Just as a craftsman selects the appropriate instrument for each task, students must discern when to apply particular algebraic strategies.

For the given trinomial \( 3x^2 - 2x - 5 \), no such pairs of numbers exist, highlighting the importance of recognizing when a trinomial is prime. Being able to identify when an expression cannot be factored can save time and direct the student towards alternate solution methods, such as completing the square or using the quadratic formula. Nevertheless, the ability to efficiently search for potential factors is integral to mastering algebra and branches further into calculus and beyond.