Chapter 4: Problem 51
Solution of the differential equation \(\frac{d y}{d x}+\frac{1+y^{2}}{\sqrt{1-x^{2}}}=0\) is (a) \(\tan ^{-1} y+\sin ^{-1} x=C\) (b) \(\tan ^{-1} x+\sin ^{-1} y=C\) (c) \(\tan ^{-1} y \cdot \sin ^{-1} x=C\) (d) \(\tan ^{-1} y-\sin ^{-1} x=C\)
Short Answer
Expert verified
(a) \(\tan^{-1} y + \sin^{-1} x = C\).
Step by step solution
01
Identify the Equation Type
The given differential equation is \( \frac{d y}{d x} + \frac{1+y^2}{\sqrt{1-x^2}} = 0 \). It is a first-order differential equation because it involves \( \frac{d y}{d x} \).
02
Rearrange the Equation
Rearrange the equation by isolating \( \frac{d y}{d x} \): \( \frac{d y}{d x} = -\frac{1+y^2}{\sqrt{1-x^2}} \).
03
Integrate Both Sides
Rewrite the equation as \( d y = -\frac{1+y^2}{\sqrt{1-x^2}} d x \). Integrate both sides: \( \int 1 d y = \int -\frac{1+y^2}{\sqrt{1-x^2}} d x \).
04
Integrate the Left Side
The integral of \( 1 d y \) is \( y \).
05
Change Variable for the Right Side
Set \( y = \tan z \), then \( dy = \sec^2 z dz \). Substitute and integrate to get \( \int \sec^2 z dz = \int -\frac{1+ an^2 z}{\sqrt{1-x^2}} d x \).
06
Simplify Using Trigonometric Identities
Since \( 1 + \tan^2 z = \sec^2 z \), it simplifies to \( \int \sec^2 z dz = \int -\sec^2 z d x/\sqrt{1-x^2} \).
07
Solve the Integral
Realize \( \int -\sec^2 z dz = -\tan^{-1} y \) and solve \( \int \frac{1}{\sqrt{1-x^2}} dx = \sin^{-1} x \).
08
Combine the Results
Combining the results of the integration \( \tan^{-1} y = -\sin^{-1} x + C \) or equivalently \( \tan^{-1} y + \sin^{-1} x = C \).
09
Choose the Correct Option
Comparing with the given options, the solution matches with option (a): \( \tan^{-1} y + \sin^{-1} x = C \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration Techniques
Integration is a fundamental operation in calculus, and it involves finding the antiderivative of a function. In this context, solving
first-order differential equations often requires integrating both sides of an equation. Here are some key techniques that are useful:
- Direct Integration: This involves integrating both sides of an equation without changing variables. It's suitable for simpler forms where the integrand is easy to work with.
- Substitution: When direct integration is challenging, substitution can help by simplifying the equation. By introducing a new variable, like letting y = tan z, the equation becomes more manageable.
- Partial Fractions: Breaking down a complex fraction into simpler parts can make integration possible when dealing with rational expressions.
First-Order Differential Equations
First-order differential equations are equations involving the first derivative of a function. Recognizing the type of differential equation is key to deciding the most appropriate method for solving it. The equation given in the exercise is an example of a first-order differential equation: \( \frac{d y}{d x} + \frac{1+y^2}{\sqrt{1-x^2}} = 0 \).
Here are some common characteristics:
Here are some common characteristics:
- They involve only the first derivative \( \frac{d y}{d x} \).
- Such equations often require rearranging before integration, which is a typical step in solving them.
Trigonometric Substitution
Trigonometric substitution is a powerful method to simplify the integration of functions involving radicals. In calculus, this technique is useful when solving integrals that involve square roots, like \( \sqrt{1 - x^2} \). Here is how it's typically applied:
- Purpose: Transform a variable in an integral using a trigonometric identity, so the resulting integral is easier to solve.
- Example: If you have \( \sqrt{1 - x^2} \), you might substitute \( x = \sin \theta \), thus simplifying the expression using the identity \( 1 - \sin^2 \theta = \cos^2 \theta \).
- Application: After substituting, integrate with respect to the new variable. Finally, reverse the substitution to express the result in terms of the original variable.