Chapter 7: Problem 56
Construct a system of nonlinear equations to describe the given behavior, then solve for the requested solutions. The squares of two numbers add to 360 . The second number is half the value of the fi st number squared. What are the numbers?
Short Answer
Expert verified
The numbers are 6, 18 and -6, 18.
Step by step solution
01
Define Variables
Let's denote the first number as \( x \), and the second number as \( y \).
02
Translate Relationships into Equations
We are given two main relationships in the problem. First, the squares of the two numbers add up to 360: \( x^2 + y^2 = 360 \). Second, the second number, \( y \), is half of the first number squared: \( y = \frac{x^2}{2} \).
03
Substitute and Simplify
Substitute the expression for \( y \) from the second equation into the first equation to eliminate \( y \):\[ x^2 + \left(\frac{x^2}{2}\right)^2 = 360 \]This simplifies to:\[ x^2 + \frac{x^4}{4} = 360 \]
04
Clear Fractions
To simplify solving the equation, multiply every term by 4 to clear the fraction:\[ 4x^2 + x^4 = 1440 \]
05
Rearrange into a Polynomial Equation
Rearrange the equation to form a quadratic in terms of \( x^2 \): \[ x^4 + 4x^2 - 1440 = 0 \]Let \( z = x^2 \), then we have a quadratic \( z^2 + 4z - 1440 = 0 \).
06
Solve the Quadratic Equation
Using the quadratic formula \( z = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \) with \( a = 1, b = 4, c = -1440 \):\[ z = \frac{-4 \pm \sqrt{4^2 - 4 \times 1 \times (-1440)}}{2 \times 1} \]\[ z = \frac{-4 \pm \sqrt{16 + 5760}}{2} \]\[ z = \frac{-4 \pm 76}{2} \]This yields \( z = 36 \) and \( z = -40 \). Since \( z = x^2 \) and must be positive, we take \( z = 36 \).
07
Find Values of x from z
Since \( x^2 = 36 \), solving gives \( x = 6 \) or \( x = -6 \).
08
Find Corresponding y Values
Use the equation \( y = \frac{x^2}{2} \) to find \( y \):- If \( x = 6 \), then \( y = \frac{36}{2} = 18 \).- If \( x = -6 \), then \( y = \frac{36}{2} = 18 \).Thus, the pairs \((x, y)\) are \((6, 18)\) and \((-6, 18)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
System of Equations
A system of equations involves more than one equation considered simultaneously. In our exercise, we have a **nonlinear system of equations**. This means that at least one of the equations in the system is not linear. For the given problem, the system is constructed from the two statements:
- The squares of two numbers add to 360: \( x^2 + y^2 = 360 \).
- The second number is half the value of the first number squared: \( y = \frac{x^2}{2} \).
Quadratic Formula
The quadratic formula is a powerful tool used to find the roots of quadratic equations, expressed as \( ax^2 + bx + c = 0 \). In this instance, we rephrase the problem to replace the role of \( x \) with \( z = x^2 \). This rearranges our equation into a more familiar quadratic form:
- \( z^2 + 4z - 1440 = 0 \)
Polynomial Equations
Polynomial equations are equations involving sums of powers of variables. In our exercise, we've ultimately simplified a complex situation into a simple polynomial equation involving \( x^2 \). Polynomial equations can have various degrees, leading to different numbers of possible solutions.
- The non-linear origin of our problem involves both quadratic (\( x^2 \)) and quartic (\( x^4 \)) terms.
- By substituting \( z = x^2 \), we translate the quartic equation into the quadratic form \( z^2 + 4z - 1440 = 0 \).
Solution of Equations
Finding the solution of an equation means determining the variable values that satisfy the equation. After calculating the potential values of \( z = x^2 \) using the quadratic formula, we find that:
- \( z = 36 \): This leads to \( x^2 = 36 \), thus \( x = 6 \) or \( x = -6 \).
- The negative value of \( z = -40 \) is discarded since a square cannot be negative.