Problem 127
Question
Use your graphing utility to graph each side of the equation in the same viewing rectangle. Then use the \(x\) -coordinate of the intersection point to find the equation's solution set Verify this value by direct substitution into the equation. $$ \log _{3}(4 x-7)=2 $$
Step-by-Step Solution
Verified Answer
The solution of the equation is \(x = 4\).
1Step 1: Graph the functions
First, graph two functions: \(y = \log _{3}(4x-7)\) and \(y = 2\) on the same graph. Identify the intersection points. The x-coordinate of this point is your solution.
2Step 2: Find the intersection point
Set \(\log _{3}(4x-7)\) equal to 2 and solve for \(x\):\n\[ log _{3}(4x-7) = 2 <=> 3^2 = 4x-7 <=> 9 = 4x-7 <=> 16 = 4x <=> x = 4 \]
3Step 3: Verify the solution
Verify this solution by substituting \(x = 4\) back into the original equation. If the left-hand side equals to the right-hand side, then the answer is correct. Substitute \(x = 4\):\n\[ \log _{3}(4*(4)-7) = \log _{3}(9) = 2\]\nSince the left-hand side equals to the right-hand side, the solution is correct.
Key Concepts
Graphing Calculator UseLogarithm PropertiesVerifying Solutions
Graphing Calculator Use
Utilizing a graphing calculator is an invaluable tool when working with logarithmic equations. It offers a visual representation that can simplify the process of understanding and solving complex problems.
For the given exercise, where the equation is \(\log _{3}(4 x-7)=2\), the graphing calculator can be used to graph each side of the equation. Firstly, enter the logarithmic function \(y = \log _{3}(4x-7)\) into your graphing calculator and graph it. Next, graph the line \(y = 2\) on the same coordinate plane. The point where these two graphs intersect represents the solution of the equation. The \(x\)-coordinate of this point precisely indicates the value of \(x\) that satisfies the original equation.
An advantage of using a graphing calculator is that it helps to confirm whether there is one solution, multiple solutions, or no solutions at all, just from the visual intersection points on the graph. Moreover, if the graphs do not intersect, this indicates that the equation has no real solutions.
For the given exercise, where the equation is \(\log _{3}(4 x-7)=2\), the graphing calculator can be used to graph each side of the equation. Firstly, enter the logarithmic function \(y = \log _{3}(4x-7)\) into your graphing calculator and graph it. Next, graph the line \(y = 2\) on the same coordinate plane. The point where these two graphs intersect represents the solution of the equation. The \(x\)-coordinate of this point precisely indicates the value of \(x\) that satisfies the original equation.
An advantage of using a graphing calculator is that it helps to confirm whether there is one solution, multiple solutions, or no solutions at all, just from the visual intersection points on the graph. Moreover, if the graphs do not intersect, this indicates that the equation has no real solutions.
Logarithm Properties
Understanding logarithm properties is essential when solving logarithmic equations. A logarithm, by definition, represents the power to which a base, say \(b\), must be raised to obtain a certain number \(x\): \(\log_b(x)\).
The exercise \(\log _{3}(4 x-7)=2\) relies on a few fundamental properties of logarithms, such as the equivalence between logarithms and their exponential forms. This relationship is expressed by the equation \(\log_b(x) = y \Leftrightarrow b^y = x\). Using this property, the given equation \(\log _{3}(4x-7) = 2\) can be rewritten in exponential form as \(3^2 = 4x - 7\).
Other important properties include the logarithm laws for multiplication, division, and exponentiation, which are helpful for combining and simplifying logarithmic expressions. For example, \(\log_b(x) + \log_b(y) = \log_b(xy)\), and \(\log_b(x) - \log_b(y) = \log_b(x/y)\). Understanding and applying these properties can make complex logarithmic equations more approachable and easier to solve.
The exercise \(\log _{3}(4 x-7)=2\) relies on a few fundamental properties of logarithms, such as the equivalence between logarithms and their exponential forms. This relationship is expressed by the equation \(\log_b(x) = y \Leftrightarrow b^y = x\). Using this property, the given equation \(\log _{3}(4x-7) = 2\) can be rewritten in exponential form as \(3^2 = 4x - 7\).
Other important properties include the logarithm laws for multiplication, division, and exponentiation, which are helpful for combining and simplifying logarithmic expressions. For example, \(\log_b(x) + \log_b(y) = \log_b(xy)\), and \(\log_b(x) - \log_b(y) = \log_b(x/y)\). Understanding and applying these properties can make complex logarithmic equations more approachable and easier to solve.
Verifying Solutions
Verifying solutions is a crucial step in confirming that your answer satisfies the original equation. After finding a potential solution using graphing or algebraic manipulation, it should be substituted back into the original logarithmic equation to ensure that both sides are equal.
In the exercise with the equation \(\log _{3}(4 x-7)=2\), the solution \(x = 4\) was obtained. To verify this, substitute \(x\) back into the equation and check if both sides match. Here, \(\log _{3}(4*(4)-7)\) simplifies to \(\log _{3}(9)\), which is indeed equal to 2 because 3, the base of the logarithm, raised to the power of 2, gives us 9 (\(3^2 = 9\)). This confirms that \(x = 4\) is the correct solution.
Verification helps prevent errors that might have occurred in the problem-solving process and is an essential habit for students to form. It's a final check to ensure the solution is not only mathematically correct but also applicable to the given problem.
In the exercise with the equation \(\log _{3}(4 x-7)=2\), the solution \(x = 4\) was obtained. To verify this, substitute \(x\) back into the equation and check if both sides match. Here, \(\log _{3}(4*(4)-7)\) simplifies to \(\log _{3}(9)\), which is indeed equal to 2 because 3, the base of the logarithm, raised to the power of 2, gives us 9 (\(3^2 = 9\)). This confirms that \(x = 4\) is the correct solution.
Verification helps prevent errors that might have occurred in the problem-solving process and is an essential habit for students to form. It's a final check to ensure the solution is not only mathematically correct but also applicable to the given problem.
Other exercises in this chapter
Problem 126
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