Chapter 1: Problem 18
If \(e^{x}=y+\sqrt{1+y^{2}}\), then \(y\) is equal to (a) \(e^{x}+e^{-x}\) (b) \(e^{x}-e^{-x}\) (c) \(\frac{1}{2}\left(e^{x}-e^{-x}\right)\) (d) \(\frac{1}{2}\left(e^{x}+e^{-x}\right)\)
Short Answer
Expert verified
The correct answer is (c) \(\frac{1}{2}(e^x - e^{-x})\).
Step by step solution
01
Substitution and Squaring
We start with the equation \(e^{x}=y+ ext{√}(1+y^{2})\). To eliminate the square root, isolate it: \(y=e^x - ext{√}(1+y^{2})\). Next, square both sides of \(e^x = y + \text{√}(1+y^{2})\): \[(e^{x})^2 = (y + ext{√}(1+y^{2}))^2\].Expand the right side to get: \[e^{2x} = y^2 + 2y ext{√}(1+y^{2}) + (1+y^{2})\].
02
Simplifying the Squared Equation
Upon simplifying the equation \[e^{2x} = y^2 + 2y ext{√}(1+y^{2}) + 1 + y^2\] , we get: \[e^{2x} = 2y^2 + 1 + 2y ext{√}(1+y^{2})\]. By rearranging terms and equating, the square root term can be isolated and squaring both sides again eliminates it, leading to a more solvable equation for \(y\).
03
Isolating Terms for Simplification
Rearrange the expression \(e^{2x} = 1 + 2y^2 + 2y\sqrt{1+y^2}\) to isolate the square root term: \(e^{2x} - 2y^2 - 1 = 2y\text{√}(1+y^{2})\). Divide both sides by 2 to get:\[\frac{e^{2x} - 1}{2} = y\text{√}(1+y^{2})\].
04
Solving for y
Using \(y=e^x-\text{√}(1+y^{2})\) and substituting \(y\) into the expression \(\frac{e^{2x} - 1}{2} = y\text{√}(1+y^{2})\), we find a potential \(y\) that fits with hyperbolic identities. Recognizing hyperbolic functions, the relation \(e^x - e^{-x} = 2y\) hints \(y = \frac{1}{2}(e^x - e^{-x})\).
05
Verifying the Solution
Upon noticing that the setup resembles hyperbolic functions, we check whether \(y = \frac{1}{2}(e^x - e^{-x})\) satisfies the given original equation \(e^x = y + \sqrt{1+y^2}\). Simplifying both sides with this \(y\) value confirms the identity matches. Thus, the solution is verified.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Differential Equations
Differential equations play a crucial role in modeling real-world phenomena. They are equations that involve derivatives of a function or functions. In essence, they describe how a quantity changes with respect to another variable, often time. This makes them indispensable in physics, engineering, economics, and biology.
Differential equations can be categorized into various types:
- Ordinary Differential Equations (ODEs), where derivatives are taken with respect to a single variable.
- Partial Differential Equations (PDEs), which involve derivatives with respect to more than one variable.
Exponential Functions
Exponential functions are mathematical expressions in the form of \(f(x) = a \, e^{bx}\), where \(e\) is Euler's number, approximately 2.71828. These functions exhibit rapid growth or decay and are pivotal in mathematical modeling. Some key properties of exponential functions include:
- The base \(e\) means that the function's growth rate doubles for every unit increase in \(x\).
- They provide a smooth, continuous curve, essential for solving differential equations effectively.
Square Root Elimination
Square roots present unique challenges in equations, often complicating the path to a solution. The process of eliminating square roots involves careful manipulation and is a frequent step in solving mathematical problems. Here's a simplified outline of how square roots might be eliminated:
- Isolate the square root term in the equation whenever possible. This helps in focusing the operations you perform next.
- Square both sides of the equation to eliminate the square root. This step must be done carefully to avoid introducing extraneous solutions.