Chapter 1: Problem 85
Solve each equation. $$6(x+2)^{4}-11(x+2)^{2}=-4$$
Short Answer
Expert verified
The solutions are \( x = -2 \pm \sqrt{\frac{4}{3}} \) and \( x = -2 \pm \sqrt{\frac{1}{2}} \).
Step by step solution
01
Introduce a substitution
Let \( y = (x + 2)^{2} \). This substitution will simplify the equation. Now, rewrite the given equation using \( y \).
02
Rewrite the equation
Substituting \( y \) into the equation, we get: \( 6y^{2} - 11y = -4 \).
03
Move all terms to one side
Add 4 to both sides to set the equation to zero: \( 6y^{2} - 11y + 4 = 0 \).
04
Factor the quadratic equation
Factorize \( 6y^{2} - 11y + 4 \) into two binomials: \( (3y-4)(2y-1) = 0 \).
05
Solve for \( y \)
Set each factor equal to zero and solve for \( y \):
06
Solve \( 3y-4 = 0 \)
Solving \( 3y-4 = 0 \) yields \( y = \frac{4}{3} \).
07
Solve \( 2y-1 = 0 \)
Solving \( 2y-1 = 0 \) yields \( y = \frac{1}{2} \).
08
Substitute back \( y = (x+2)^{2} \)
Now, substitute back \( y \) into the original substitution. So, \( (x+2)^{2} = \frac{4}{3} \) or \( (x+2)^{2} = \frac{1}{2} \).
09
Solve for \( x \) from \( (x+2)^{2} = \frac{4}{3} \)
Taking the square root of both sides, we get \( x + 2 = \pm \sqrt{\frac{4}{3}} \). This simplifies to two solutions: \( x = -2 \pm \sqrt{\frac{4}{3}} \).
10
Solve for \( x \) from \( (x+2)^{2} = \frac{1}{2} \)
Taking the square root of both sides, we get \( x + 2 = \pm \sqrt{\frac{1}{2}} \). This simplifies to two solutions: \( x = -2 \pm \sqrt{\frac{1}{2}} \).
11
Write the final solutions
The final solutions for the given equation are: \( x = -2 + \sqrt{\frac{4}{3}} \), \( x = -2 - \sqrt{\frac{4}{3}} \), \( x = -2 + \sqrt{\frac{1}{2}} \), and \( x = -2 - \sqrt{\frac{1}{2}} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Substitution Method
The substitution method is a powerful technique to simplify complicated equations. By introducing a new variable, we can turn a complex problem into a simpler one. For instance, in the problem, we let \( y = (x + 2)^{2} \). This changes the original equation into a quadratic form: \( 6y^{2} - 11y = -4 \). The new equation is easier to handle because it is a standard quadratic. This method is especially useful when dealing with polynomial or rational equations. By replacing parts of the equation with a new variable, we simplify the original expression, making it easier to solve.
Factoring Quadratics
Factoring quadratics is a technique used to break down a quadratic equation into simpler, solvable parts. After substitution, the equation became \( 6y^{2} - 11y + 4 = 0 \). We then factored it into \( (3y-4)(2y-1) = 0 \). Factoring makes it easy to find the solutions: set each factor to zero and solve for \( y \). This process involves:
- Finding two numbers that multiply to the constant term (in this case, 4) and add to the coefficient of the middle term (in this case, -11).
- Using these numbers to break the middle term and factor by grouping.
Completing the Square
Completing the square is a method to solve quadratic equations by transforming them into a perfect square trinomial. Although this method was not directly used in our problem, it's another way to solve quadratics. To complete the square:
- Ensure the quadratic equation is in the form \( ax^2 + bx + c = 0 \).
- Move the constant term to the other side: \( ax^2 + bx = -c \).
- If \( a \) is not 1, divide the entire equation by \( a \).
- Add and subtract \( \left( \frac{b}{2a} \right)^2 \) inside the equation.
- Rewrite the left side as a square of a binomial.
Radical Expressions
Radical expressions involve numbers and variables under the radical sign. In our solved problem, after substituting back, we ended up with \( (x + 2)^{2} = \frac{4}{3} \) and \( (x + 2)^{2} = \frac{1}{2} \). Solving these required taking the square root of both sides:
- \( x + 2 = \pm \sqrt{\frac{4}{3}} \)
- \( x + 2 = \pm \sqrt{\frac{1}{2}} \)