Chapter 8: Problem 34
Solve each equation. \(x^{2 / 3}-7 x^{1 / 3}+12=0\)
Short Answer
Expert verified
The solutions are \(x = 27\) and \(x = 64\).
Step by step solution
01
Substitution
Let \( y = x^{1/3} \). This implies that \( y^2 = (x^{1/3})^2 = x^{2/3} \). Substitute these into the equation to get a quadratic equation in terms of \( y \): \( y^2 - 7y + 12 = 0 \).
02
Solve the Quadratic Equation
Factor the quadratic equation \( y^2 - 7y + 12 = 0 \). Notice that it factors to \((y - 3)(y - 4) = 0\).
03
Find the Solutions for y
Using the factored form \((y - 3)(y - 4) = 0\), set each factor equal to zero: \(y - 3 = 0\) and \(y - 4 = 0\). Solving these gives \( y = 3 \) and \( y = 4 \).
04
Back Substitution
Recall that \( y = x^{1/3} \). Substitute \( y = 3 \) back to get \( x^{1/3} = 3 \). Cubing both sides gives \( x = 3^3 = 27 \). Now substitute \( y = 4 \) into \( y = x^{1/3} \) to get \( x^{1/3} = 4 \). Cubing both sides here gives \( x = 4^3 = 64 \).
05
Verification
Verify both solutions by substituting them back into the original equation \( x^{2/3} - 7x^{1/3} + 12 = 0\). For \( x = 27 \): \( 27^{2/3} - 7 \times 27^{1/3} + 12 = 0 \). For \( x = 64 \): \( 64^{2/3} - 7 \times 64^{1/3} + 12 = 0 \). Both satisfy the equation, confirming that both are correct.
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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 tool for simplifying complex equations by introducing a new variable. When faced with an equation involving a term like \(x^{2/3}\), it can be helpful to switch perspectives by defining a new variable. For instance, we can let \(y = x^{1/3}\), transforming our original equation into a simpler form that’s easier to handle.
- By substituting \(y = x^{1/3}\), we automatically also set \(y^2 = x^{2/3}\).
- This change of variable helps reduce the complexity, turning the equation into a typical quadratic form: \(y^2 - 7y + 12 = 0\).
Factoring Quadratics
Factoring quadratics is a fundamental algebraic skill used to solve quadratic equations like \(y^2 - 7y + 12 = 0\). The quadratic equation needs to be arranged into a form where it can be expressed as the product of two binomials.
- For the quadratic \(y^2 - 7y + 12\), look for two numbers that multiply to 12 (the constant term) and add to -7 (the coefficient of y).
- These numbers are -3 and -4, which means the quadratic factors as \((y - 3)(y - 4) = 0\).
Back Substitution
Back substitution is the process of returning to the original variable after solving a simpler equation. Once we’ve solved the quadratic equation from the substitution phase, we need to find the corresponding values for the initial variable, \(x\).
- Solving \((y - 3)(y - 4) = 0\) gives us \(y = 3\) or \(y = 4\).
- Remembering that \(y = x^{1/3}\), we substitute back: for \(y = 3\), we have \(x^{1/3} = 3\), which gives \(x = 27\).
- Similarly, for \(y = 4\), we set \(x^{1/3} = 4\), resulting in \(x = 64\).