Mathematics
Grade 11
15 min
Rational root theorem
Rational root theorem
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1
Introduction & Learning Objectives
Learning Objectives
State the Rational Root Theorem with precision.
Identify all possible rational roots of a polynomial with integer coefficients.
Use synthetic division to efficiently test potential rational roots.
Find all actual rational roots of a given polynomial.
Factor a polynomial completely using the roots found via the Rational Root Theorem.
Solve polynomial equations by finding their rational roots.
Explain the roles of the leading coefficient and constant term in determining possible roots.
How can you find the roots of a complex polynomial like 3x³ + 4x² - 5x - 2 = 0 without just guessing? 🤔
The Rational Root Theorem provides a powerful and systematic method to find a list of all *possible* rational roots of a polynomial. This narrows down the search immens...
2
Key Concepts & Vocabulary
TermDefinitionExample
Polynomial with Integer CoefficientsA polynomial where all coefficients (the numbers in front of the variables) and the constant term are integers.P(x) = 4x³ - 2x² + 5x - 10 is a polynomial with integer coefficients. P(x) = 1/2x² + 3 is not.
Root (or Zero)A value 'c' for the variable x such that the polynomial evaluates to zero, i.e., P(c) = 0. Roots are the x-intercepts of the polynomial's graph.For P(x) = x² - 9, the roots are x = 3 and x = -3 because (3)² - 9 = 0 and (-3)² - 9 = 0.
Rational NumberAny number that can be expressed as a fraction p/q, where p and q are integers and q is not zero.Examples include 5 (which is 5/1), -2/3, and 0.75 (which is 3/4).
Constant Term (a₀)The term in a polynomial that does not have a variable attached to it.In the...
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Core Formulas
The Rational Root Theorem
If a polynomial P(x) = a_n x^n + a_{n-1} x^{n-1} + ... + a_1 x + a_0 has integer coefficients, then every rational root of P(x) is of the form p/q, where p is an integer factor of the constant term a_0 and q is an integer factor of the leading coefficient a_n.
Use this theorem to generate a finite list of all possible rational roots for a polynomial. This is the starting point for finding the actual roots.
The Factor Theorem
A number 'c' is a root of a polynomial P(x) if and only if (x - c) is a factor of P(x).
This theorem connects finding roots to factoring polynomials. Once you confirm 'c' is a root (e.g., using synthetic division), you know that (x - c) is one of the factors.
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Easy
According to the Rational Root Theorem, for a polynomial with integer coefficients, any rational root must be of the form p/q. What do 'p' and 'q' represent?
A.p is a factor of the leading coefficient, and q is a factor of the constant term.
B.p is a factor of the constant term, and q is a factor of the leading coefficient.
C.p is a factor of the highest degree term, and q is a factor of the lowest degree term.
D.p is any integer, and q is any non-zero integer.
Easy
For the polynomial P(x) = 4x³ - 2x² + 5x - 10, which of the following sets represents all possible integer factors 'p' of the constant term?
A.{1, 2, 5, 10}
B.{±1, ±2, ±4}
C.{±1, ±2, ±5, ±10}
D.{±1, ±1/2, ±1/4}
Easy
For the polynomial P(x) = 2x³ + 3x² - 8x + 3, which set represents all possible integer factors 'q' of the leading coefficient?
A.{±1, ±3}
B.{±1, ±2}
C.{1, 2}
D.{±1, ±2, ±3}
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