Chapter 3: Problem 75
Find the zeros of the function algebraically. Give exact answers. $$f(x)=x^{2}-5 x+1$$
Short Answer
Expert verified
The zeros are \( x = \frac{5 + \sqrt{21}}{2} \) and \( x = \frac{5 - \sqrt{21}}{2} \).
Step by step solution
01
- Identify the Quadratic Formula
To find the zeros of a quadratic function, use the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]In this formula, \( a \), \( b \), and \( c \) are coefficients from the standard quadratic form \( ax^2 + bx + c \).
02
- Determine Coefficients
For the function \( f(x) = x^2 - 5x + 1 \), identify the coefficients:\[ a = 1, \ b = -5, \ c = 1 \]
03
- Substitute Coefficients into Quadratic Formula
Substitute the values of \( a \), \( b \), and \( c \) into the quadratic formula:\[ x = \frac{-(-5) \pm \sqrt{(-5)^2 - 4 \cdot 1 \cdot 1}}{2 \cdot 1} \]
04
- Simplify the Expression Inside the Square Root
Simplify the expression inside the square root (the discriminant):\[ x = \frac{5 \pm \sqrt{25 - 4}}{2} \]\[ x = \frac{5 \pm \sqrt{21}}{2} \]
05
- Simplify the Entire Expression
Divide the terms in the numerator by the denominator to get the final zeros:\[ x = \frac{5 + \sqrt{21}}{2} \] \[ x = \frac{5 - \sqrt{21}}{2} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic formula
The quadratic formula is a powerful tool used to find the zeros (or roots) of a quadratic equation. A quadratic equation is typically written as \( ax^2 + bx + c = 0 \), where \( a \), \( b \), and \( c \) are constants. The quadratic formula is given by: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] This formula works for all quadratic equations and guarantees solutions if they exist. To use this formula, simply identify the coefficients \( a \), \( b \), and \( c \) from your quadratic equation, substitute them into the formula, and then simplify. It covers all cases: real, repeated, and complex roots.
discriminant
The discriminant is a part of the quadratic formula located under the square root: \( \sqrt{b^2 - 4ac} \). It is crucial because it determines the nature of the roots of the quadratic equation. There are three primary cases based on the value of the discriminant:
- If the discriminant \( b^2 - 4ac \) is greater than 0, there are two distinct real roots.
- If the discriminant is equal to 0, there is exactly one real root (also called a repeated or double root).
- If the discriminant is less than 0, the equation has two complex roots.
solving quadratic equations
To solve a quadratic equation and find its zeros, follow these steps:
- Write in Standard Form: Ensure the quadratic equation is in the form \( ax^2 + bx + c = 0 \).
- Identify Coefficients: Recognize the values of \( a \), \( b \), and \( c \).
- Apply the Quadratic Formula: Substitute these coefficients into the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \).
- Simplify the Solution: Calculate the discriminant and simplify the expression to find the zeros.