1.4 problem 4

Internal problem ID [4]
Internal file name [OUTPUT/4_Sunday_June_05_2022_01_33_37_AM_33243587/index.tex]

Book: Differential equations and linear algebra, 3rd ed., Edwards and Penney
Section: Section 1.2. Integrals as general and particular solutions. Page 16
Problem number: 4.
ODE order: 1.
ODE degree: 1.

The type(s) of ODE detected by this program : "quadrature"

Maple gives the following as the ode type

[_quadrature]

\[ \boxed {y^{\prime }=\frac {1}{x^{2}}} \] With initial conditions \begin {align*} [y \left (1\right ) = 5] \end {align*}

1.4.1 Existence and uniqueness analysis

This is a linear ODE. In canonical form it is written as \begin {align*} y^{\prime } + p(x)y &= q(x) \end {align*}

Where here \begin {align*} p(x) &=0\\ q(x) &=\frac {1}{x^{2}} \end {align*}

Hence the ode is \begin {align*} y^{\prime } = \frac {1}{x^{2}} \end {align*}

The domain of \(p(x)=0\) is \[ \{-\infty

1.4.2 Solving as quadrature ode

Integrating both sides gives \begin {align*} y &= \int { \frac {1}{x^{2}}\,\mathop {\mathrm {d}x}}\\ &= -\frac {1}{x}+c_{1} \end {align*}

Initial conditions are used to solve for \(c_{1}\). Substituting \(x=1\) and \(y=5\) in the above solution gives an equation to solve for the constant of integration. \begin {align*} 5 = c_{1} -1 \end {align*}

The solutions are \begin {align*} c_{1} = 6 \end {align*}

Trying the constant \begin {align*} c_{1} = 6 \end {align*}

Substituting this in the general solution gives \begin {align*} y&=\frac {-1+6 x}{x} \end {align*}

The constant \(c_{1} = 6\) gives valid solution.

Summary

The solution(s) found are the following \begin{align*} \tag{1} y &= \frac {-1+6 x}{x} \\ \end{align*}

(a) Solution plot

(b) Slope field plot

Verification of solutions

\[ y = \frac {-1+6 x}{x} \] Verified OK.

1.4.3 Maple step by step solution

\[ \begin {array}{lll} & {} & \textrm {Let's solve}\hspace {3pt} \\ {} & {} & \left [y^{\prime }=\frac {1}{x^{2}}, y \left (1\right )=5\right ] \\ \bullet & {} & \textrm {Highest derivative means the order of the ODE is}\hspace {3pt} 1 \\ {} & {} & y^{\prime } \\ \bullet & {} & \textrm {Integrate both sides with respect to}\hspace {3pt} x \\ {} & {} & \int y^{\prime }d x =\int \frac {1}{x^{2}}d x +c_{1} \\ \bullet & {} & \textrm {Evaluate integral}\hspace {3pt} \\ {} & {} & y=-\frac {1}{x}+c_{1} \\ \bullet & {} & \textrm {Solve for}\hspace {3pt} y \\ {} & {} & y=\frac {c_{1} x -1}{x} \\ \bullet & {} & \textrm {Use initial condition}\hspace {3pt} y \left (1\right )=5 \\ {} & {} & 5=c_{1} -1 \\ \bullet & {} & \textrm {Solve for}\hspace {3pt} c_{1} \\ {} & {} & c_{1} =6 \\ \bullet & {} & \textrm {Substitute}\hspace {3pt} c_{1} =6\hspace {3pt}\textrm {into general solution and simplify}\hspace {3pt} \\ {} & {} & y=\frac {-1+6 x}{x} \\ \bullet & {} & \textrm {Solution to the IVP}\hspace {3pt} \\ {} & {} & y=\frac {-1+6 x}{x} \end {array} \]

Maple trace

`Methods for first order ODEs: 
--- Trying classification methods --- 
trying a quadrature 
<- quadrature successful`
 

✓ Solution by Maple

Time used: 0.0 (sec). Leaf size: 11

dsolve([diff(y(x),x) = 1/x^2,y(1) = 5],y(x), singsol=all)
 

\[ y \left (x \right ) = -\frac {1}{x}+6 \]

✓ Solution by Mathematica

Time used: 0.002 (sec). Leaf size: 12

DSolve[{y'[x] == 1/x^2,y[1]==5},y[x],x,IncludeSingularSolutions -> True]
 

\[ y(x)\to 6-\frac {1}{x} \]