Chapter 11: Problem 49
Solve each equation. Check your solutions. $$ x^{4}-29 x^{2}+100=0 $$
Short Answer
Expert verified
The solutions are \( x = \pm 5 \) and \( x = \pm 2 \).
Step by step solution
01
- Make a Substitution
Let's start by making a substitution to simplify the equation. Let’s set \( u = x^2 \). Therefore, the original equation becomes \( u^2 - 29u + 100 = 0 \).
02
- Solve the Quadratic Equation
Now, solve the quadratic equation \( u^2 - 29u + 100 = 0 \). To factor this, we look for two numbers that multiply to 100 and add up to -29. These numbers are -25 and -4. Therefore, the equation factors as \( (u - 25)(u - 4) = 0 \).
03
- Solve for u
Now set each factor equal to zero and solve for \( u \): \( u - 25 = 0 \) gives \( u = 25 \), and \( u - 4 = 0 \) gives \( u = 4 \).
04
- Substitute Back for x
Recall that \( u = x^2 \). So, substitute back to get \( x^2 = 25 \) and \( x^2 = 4 \).
05
- Solve for x
Solve these equations for \( x \): \( x^2 = 25 \) gives \( x = \pm 5 \), and \( x^2 = 4 \) gives \( x = \pm 2 \).
06
- Check Solutions
Check these solutions by substituting back into the original equation: \( x = 5, -5, 2, -2 \). For \( x = 5 \), \( 5^4 - 29 \times 5^2 + 100 = 0 \), for \( x = -5 \), \( (-5)^4 - 29 \times (-5)^2 + 100 = 0 \), for \( x = 2 \), \( 2^4 - 29 \times 2^2 + 100 = 0 \), and for \( x = -2 \), \( (-2)^4 - 29 \times (-2)^2 + 100 = 0 \). All checks confirm the solutions.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic substitution
To simplify the process of solving polynomial equations, especially higher-degree ones, we can use quadratic substitution. This method helps convert a complex polynomial into a simpler quadratic equation that we can easily work with. In our exercise, we began with the equation: \( x^4 - 29x^2 + 100 = 0 \). By setting \( u = x^2 \), we transformed it into a quadratic form: \( u^2 - 29u + 100 = 0 \). This substitution reduces the complexity of our original equation, providing an easier pathway to solution.
factoring quadratic equations
Once we have a quadratic equation like \( u^2 - 29u + 100 = 0 \), we can solve it by factoring. Factoring involves finding two numbers that multiply to the constant term (100) and add up to the linear coefficient (-29). In this case, the suitable numbers are -25 and -4. By expressing the equation in factored form, we get:\( (u - 25)(u - 4) = 0 \). Now we can set each factor equal to zero and solve for \( u \): \( u - 25 = 0 \) gives \( u = 25 \), and \( u - 4 = 0 \) gives \( u = 4 \).
solving higher-degree polynomials
After solving the quadratic equation, we need to return to our original variable \( x \). Recalling that \( u = x^2 \), we substitute back and solve for \( x \). The values of \( u \) that we obtained are 25 and 4, so we set up the equations: \( x^2 = 25 \) and \( x^2 = 4 \). By solving these, we find:- \( x = \,pm 5 \).- \( x = \,pm 2 \).Therefore, the solutions to the original polynomial equation are \( x = 5, -5, 2, \,and -2 \). Verifying these solutions by substituting them back into the original equation confirms their correctness.