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TK-124 Matematika Teknik Kimia I

Basic Concepts and Classifying


Differential Equations

First Order Differential Equations

Dicky Dermawan
dickydermawan@gmail.com
Modeling with Differential Equations

Perhaps the most important of all the applications of


calculus
is differential equations.

When physical scientists or social scientists use


calculus, more often than not it is to analyze a
differential equation that has arisen in the process of
modeling some phenomenon that they are studying.

Although it is often impossible to find an explicit


formula for the solution of a differential equation, we
will see that graphical and numerical approaches
Differential Equations
A differential equation is an equation involving an
unknown function and its derivatives.
A differential
equation is an
ordinary differential
equation if the
unknown
function depends on
only one
independent
variable. If the
unknown function
depends on two or
more independent
Order & Solution
The order of a differential equation is the order of the
highest derivative appearing in the equation.
A solution of a differential equation in the unknown
function y and the independent variable x on the
interval is a function y(x) that satisfies the differential
equation identically for all x in .

Some differential equations have infinitely many solutions,


whereas other differential equations have no solutions. It is
also possible that a differential equation has exactly one
solution.
The general solution of a differential equation is the set of
all solutions.
Initial-Value vs Boundary-Value
Problems
A differential equation along with subsidiary conditions
on the unknown function and its derivatives, all given
at the same value of the independent variable,
constitutes an initial-value problem. The subsidiary
conditions are initial conditions.

If the subsidiary conditions are given at more than one


value of the independent variable, the problem is a
boundary-value problem
and the conditions are boundary conditions.
Standard and Differential
Forms
Standard form for a first-order differential equation in
the unknown function y(x) is

Differential form
First-Order Differential Equations
Linear Equations
Bernoulli Equations
Homogeneous Equations
Separable Equations
Exact Equations
Linear Equations
A differential equation in standard form

is linear if f(x,y)= p(x)y+q(x). First-order linear


differential equations can always be expressed as

An integrating factor for Equation 1.8 is

which depends only on x and is independent of y.


When both sides of 1.8 are multiplied by I(x), the
resulting equation
Bernoulli Equations
A Bernoulli differential equation is an equation of the
form

where n denotes a real number.


When n = 1 or n = 0, a Bernoulli equation reduces to a
linear equation.
Homogeneous Equations
A differential equation in standard form

is homogeneous if

for every real number t.


In the general framework of differential equations, the
word homogeneous has an entirely different
meaning. Only in the context of first-order differential
equations does homogeneous have the meaning
defined above.
Soal
Separable Equations
Consider a differential equation in differential form:

If M(x,y) = A(x) (a function only of x) and N(x,y) = B(y)


(a function only of y), the differential equation is
separable, or has its variables separated.
The general solution to the first-order separable
differential equation:

is

where c represents an arbitrary constant.


Exact Equations
A differential equation in differential form

is exact if

Method of Solution: first solve the equations

and

for g(x, y). The solution is then given implicitly by


Determine the ODEs classification
Write the given differential equations in
standard form

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