Identify the dependent and independent variables of the following differential equations. Give the order of the equations and state which are linear. (a) \(\frac{\mathrm{d} y}{\mathrm{~d} x}+9 y=0\) (b) \(\left(\frac{\mathrm{d} y}{\mathrm{~d} x}\right)\left(\frac{\mathrm{d}^{2} y}{\mathrm{~d} x^{2}}\right)+3 \frac{\mathrm{d} y}{\mathrm{~d} x}=0\) (c) \(\frac{\mathrm{d}^{3} x}{\mathrm{~d} t^{3}}+5 \frac{\mathrm{d} x}{\mathrm{~d} t}=\sin x\)

Short Answer

Expert verified
Question: Identify the dependent and independent variables, the order of the equation, and whether the equation is linear or not for the following differential equations: (a) \( \frac{\mathrm{d} y}{\mathrm{~d} x}+9 y=0\), (b) \(\left(\frac{\mathrm{d} y}{\mathrm{~d} x}\right)\left(\frac{\mathrm{d}^{2} y}{\mathrm{~d} x^{2}}\right)+3 \frac{\mathrm{d} y}{\mathrm{~d} x}=0\), and (c) \(\frac{\mathrm{d}^{3} x}{\mathrm{~d} t^{3}}+5 \frac{\mathrm{d} x}{\mathrm{~d} t}=\sin x\). Answer: (a) Dependent variable: \(y\), Independent variable: \(x\), Order: 1, Linearity: Linear (b) Dependent variable: \(y\), Independent variable: \(x\), Order: 2, Linearity: Nonlinear (c) Dependent variable: \(x\), Independent variable: \(t\), Order: 3, Linearity: Linear

Step by step solution

01

Dependent variable

In the first equation, the dependent variable is \(y\) as it depends on the independent variable, \(x\).
02

Independent variable

In this equation, the independent variable is \(x\). #Part (a): Order of Differential Equation#
03

Order of Equation

Since the highest derivative appearing in the equation is the first derivative, the equation is of order 1. #Part (a): Linearity#
04

Linearity

The given equation is linear because it involves only linear terms with respect to the dependent variable y and its derivatives. #Part (b): Dependent & Independent Variables#
05

Dependent variable

In the second equation, the dependent variable is \(y\) as it depends on the independent variable, \(x\).
06

Independent variable

In this equation, the independent variable is \(x\). #Part (b): Order of Differential Equation#
07

Order of Equation

Since the highest derivative appearing in the equation is the second derivative \( \frac{\mathrm{d}^{2} y}{\mathrm{~d} x^{2}}\), the equation is of order 2. #Part (b): Linearity#
08

Linearity

The given equation is nonlinear because it involves a product of the first and second derivatives of the dependent variable y. #Part (c): Dependent & Independent Variables#
09

Dependent variable

In the third equation, the dependent variable is \(x\) as it depends on the independent variable, \(t\).
10

Independent variable

In this equation, the independent variable is \(t\). #Part (c): Order of Differential Equation#
11

Order of Equation

Since the highest derivative appearing in the equation is the third derivative \(\frac{\mathrm{d}^{3} x}{\mathrm{~d} t^{3}}\), the equation is of order 3. #Part (c): Linearity#
12

Linearity

The given equation is linear because it involves only linear terms with respect to the dependent variable x and its derivatives.

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Most popular questions from this chapter

The charge, \(q\), on a capacitor in an \(L C R\) series circuit satisfies the second-order differential equation $$ L \frac{\mathrm{d}^{2} q}{\mathrm{~d} t^{2}}+R \frac{\mathrm{d} q}{\mathrm{~d} t}+\frac{1}{C} q=E $$ where \(L, R, C\) and \(E\) are constants. Show that if \(2 L=C R^{2}\) the general solution of this equation is $$ \begin{aligned} &q= \\ &\mathrm{e}^{-t /(C R)}\left(A \cos \frac{1}{C R} t+B \sin \frac{1}{C R} t\right)+C E \end{aligned} $$ If \(i=\frac{\mathrm{d} q}{\mathrm{~d} t}=0\) and \(q=0\) when \(t=0\) show that the current in the circuit is $$ i=\frac{2 E}{R} \mathrm{e}^{-t /(C R)} \sin \frac{1}{C R} t $$

Use an integrating factor to obtain the general solution of \(i R+L \frac{\mathrm{d} i}{\mathrm{~d} t}=\sin \omega t\) where \(R, L\) and \(\omega\) are constants.

Use Euler's method to find a numerical solution of \(\frac{\mathrm{dy}}{\mathrm{d} x}=\frac{x y}{x^{2}+2}\) subject to \(y(1)=3\). Take \(h=0.1\) and hence approximate \(y(1.5)\). Obtain the true solution using the method of separation of variables. Work throughout to six decimal places.

Show that \(x(t)=7 \cos 3 t-2 \sin 2 t\) is a solution of $$ \frac{\mathrm{d}^{2} x}{\mathrm{~d} t^{2}}+2 x=-49 \cos 3 t+4 \sin 2 t $$

Find the general solution of the following equations: (a) \(\frac{\mathrm{d} y}{\mathrm{~d} x}=k x\) (b) \(\frac{\mathrm{d} y}{\mathrm{~d} x}=-k y\) (c) \(\frac{\mathrm{d} y}{\mathrm{~d} x}=y^{2}\) (d) \(y \frac{d y}{d x}=\sin x\) (e) \(y \frac{\mathrm{d} y}{\mathrm{~d} x}=x+2\) (f) \(x^{2} \frac{\mathrm{d} y}{\mathrm{~d} x}=2 y^{2}+y x\) (g) \(\frac{\mathrm{d} x}{\mathrm{~d} t}=\frac{t^{4}}{x^{5}}\)

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