Chapter 9: Problem 11
Give all solutions of each nonlinear system of equations, including those with nonreal complex components. $$\begin{aligned} &y=x^{2}-2 x+1\\\ &x-3 y=-1 \end{aligned}$$
Short Answer
Expert verified
The solutions are \( \left(\frac{1}{3}, \frac{4}{9}\right) \) and \( (2, 1) \).
Step by step solution
01
Solve the first equation for y
The first equation is given by \[ y = x^2 - 2x + 1 \]Rewriting this equation explicitly, we have:\[ y = (x-1)^2 \]
02
Substitute y in the second equation
Replace the value of \( y \) from the first equation into the second equation:\[ x - 3((x-1)^2) = -1 \]This substitution gives us the equation solely in terms of \( x \).
03
Simplify and solve for x
Simplify the equation:\[ x - 3(x^2 - 2x + 1) = -1 \]Expand the terms:\[ x - 3x^2 + 6x - 3 = -1 \]Combine like terms:\[ -3x^2 + 7x - 3 = -1 \]Move all terms to one side of the equation:\[ -3x^2 + 7x - 2 = 0 \]Solve the quadratic equation. By using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \) with \( a = -3 \), \( b = 7 \), and \( c = -2 \):\[ x = \frac{-7 \pm \sqrt{7^2 - 4(-3)(-2)}}{2(-3)} \]\[ x = \frac{-7 \pm \sqrt{49 - 24}}{-6} \]\[ x = \frac{-7 \pm \sqrt{25}}{-6} \]\[ x = \frac{-7 \pm 5}{-6} \]This gives us two solutions for \( x \):\[ x = \frac{-7 + 5}{-6} = \frac{-2}{-6} = \frac{1}{3} \]\[ x = \frac{-7 - 5}{-6} = \frac{-12}{-6} = 2 \]
04
Find corresponding y values
Substitute \( x = \frac{1}{3} \) and \( x = 2 \) back into the equation \( y = (x-1)^2 \):For \( x = \frac{1}{3} \):\[ y = \left(\frac{1}{3} - 1\right)^2 = \left(-\frac{2}{3}\right)^2 = \frac{4}{9} \]For \( x = 2 \):\[ y = (2-1)^2 = 1 \]
05
Write the final solutions
The solutions to the system of equations are given by the pairs:\( \left(\frac{1}{3}, \frac{4}{9}\right) \) and \( (2, 1) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic equations
Understanding quadratic equations is crucial for solving nonlinear systems. A quadratic equation is any equation that can be written in the form \( ax^2 + bx + c = 0 \), where \( a, b, \) and \( c \) are constants and \( a eq 0 \). In our nonlinear system, the first equation is quadratic: \( y = x^2 - 2x + 1 \). Quadratic equations have curved graphs called parabolas. These parabolas can open upwards or downwards, depending on the sign of the coefficient \( a \). When solving quadratic equations within a system, ensure to understand the quadratic nature to appropriately solve and interpret the results.
substitution method
One efficient way to solve a nonlinear system of equations, like ours, is through the substitution method. First, solve one equation for one variable. In our exercise, we solved the first equation for \( y \), giving us \( y = (x-1)^2 \). Substitute this expression into the other equation. This reduces our system to a single equation in one variable. It's like peeling an onion layer by layer: eliminating one variable allows us to focus on solving for the other. Be careful during substitution to simplify correctly to avoid mistakes.
complex solutions
Sometimes, solving a quadratic equation within a nonlinear system leads to complex solutions. Complex solutions appear when the discriminant (\( b^2 - 4ac \)) in the quadratic formula is negative. Complex numbers have a real part and an imaginary part (\( i \)), where \( i \) is defined as \( \sqrt{-1} \). In our exercise, we found real solutions, but always check the discriminant to determine if complex solutions arise. For example, if the discriminant were negative: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] would yield complex numbers.
quadratic formula
The quadratic formula is an essential tool for solving quadratic equations. It is given by: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]. Let's break it down: \( b^2 - 4ac \) is called the discriminant. The discriminant tells us the nature of the roots. If positive, we get two real solutions; if zero, one real solution; if negative, two complex solutions. In our exercise, using the quadratic formula with \( a = -3 \), \( b = 7 \), and \( c = -2 \) led us to the solutions \( x = 2 \) and \( x = \frac{1}{3} \). Always plug in the respective \( a, b, \) and \( c \) values carefully to avoid computational errors.