Chapter 7: Problem 37
For the following exercises, use any method to solve the nonlinear system. $$x^{2}+y^{2}-6 y=7$$ $$\quad\quad x^{2}+y=1$$
Short Answer
Expert verified
The solution for \( y \) is \( y = \frac{7 \pm \sqrt{73}}{2} \). Corresponding \( x \) values should be found numerically.
Step by step solution
01
Rewrite Equations
First, we'll rewrite the given system of equations:\[ x^2 + y^2 - 6y = 7 \] and \[ x^2 + y = 1 \] so that we can work more easily with them. Notice the second equation can be rearranged to isolate \( x^2 \): \[ x^2 = 1 - y \]
02
Substitute for \(x^2\)
Now that we have \( x^2 = 1 - y \), substitute this expression into the first equation: \[ 1 - y + y^2 - 6y = 7 \]
03
Simplify the Substituted Equation
Simplify the equation from Step 2: \[ y^2 - 6y + 1 - y = 7 \]Combine the \(y\) terms:\[ y^2 - 7y + 1 = 7 \]Subtract 7 from both sides:\[ y^2 - 7y - 6 = 0 \]
04
Solve the Quadratic Equation
Use the quadratic formula to solve \( y^2 - 7y - 6 = 0 \) where \(a = 1\), \(b = -7\), and \(c = -6\):\[ y = \frac{-(-7) \pm \sqrt{(-7)^2 - 4 \cdot 1 \cdot (-6)}}{2 \cdot 1} \]\[ y = \frac{7 \pm \sqrt{49 + 24}}{2} \]\[ y = \frac{7 \pm \sqrt{73}}{2} \]
05
Find Corresponding \(x\) Values
We found solutions for \( y \). Use these in \( x^2 = 1 - y \) to find \( x \):1. For \( y = \frac{7 + \sqrt{73}}{2} \): \[ x^2 = 1 - \left(\frac{7 + \sqrt{73}}{2}\right) \]2. For \( y = \frac{7 - \sqrt{73}}{2} \): \[ x^2 = 1 - \left(\frac{7 - \sqrt{73}}{2}\right) \] Solve each of these for \( x \).
06
Solve for \(x\) Numerically
To solve for \( x \) numerically use the values obtained for \( y \): 1. Substitute \( y = \frac{7 + \sqrt{73}}{2} \) into \( x^2 = 1 - y \) and simplify.2. Substitute \( y = \frac{7 - \sqrt{73}}{2} \) into \( x^2 = 1 - y \) and simplify.Finally, obtain the square roots to find the potential \( x \) values corresponding to each value of \( y \).
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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 for finding the roots of a quadratic equation, which has the standard form: \[ ax^2 + bx + c = 0 \]When dealing with quadratic equations, the quadratic formula offers a way to find solutions by solving for \( x \):\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]This equation helps resolve problems involving any quadratic equation by identifying when solutions exist and what they are.Key Points:
- The term \( b^2 - 4ac \) inside the square root is called the discriminant and dictates the nature of the roots.
- If the discriminant is positive, the quadratic equation has two distinct real roots.
- If it is zero, there is one real double root.
- If the discriminant is negative, the roots are complex and non-real.
Substitution Method
The substitution method is an effective strategy for solving systems of equations, especially when one of the equations can easily be solved for one variable. It involves replacing a variable in one equation with an expression derived from another equation.For example, in our exercise:
- We start with two equations: \[ x^2 + y^2 - 6y = 7 \] and \[ x^2 + y = 1 \].
- Rearrange the second equation to isolate \( x^2 \): \[ x^2 = 1 - y \].
- Substitute \( 1 - y \) for \( x^2 \) in the first equation, leading to a quadratic in \( y \).
Solving Quadratic Equations
When solving quadratic equations, like the transformed \( y^2 - 7y - 6 = 0 \) from our exercise, several methods can be applied, including factoring, using the quadratic formula, and completing the square. Our exercise uses the quadratic formula due to its wide applicability.Here’s a basic outline of solving quadratic equations:
- Factoring: Break down the equation to factors that multiply to the original quadratic. But it may not always be possible.
- Quadratic Formula: As explained earlier, it provides an algebraic solution when factoring is not straightforward.
- Completing the Square: Rewriting the quadratic in a perfect square form to make it easier to solve.