Method Homogeneous Equations Reducible to separable
Jan 15, 2016
Method
Homogeneous EquationsReducible to separable
Chapter 2 2
Homogenous Differential Equations
A differential equation
Homogenous differential equation if
every t, where t R
isyxfdx
dy ),(
, , nf tx ty t f x y for
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Chapter 2 3
Example:1. Show that differential equation is homogenous differential equation.
dxyxxydy 22
Solution: xy
yx
dx
dy 22
xy
yxyxf
22
,
xyt
ytxttytxf
2
2222
,
2 2 2 2 2
2,
t x y x yf x y
t xy xy
Differential equation is homogeneous
Differential equation is homogeneous
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Chapter 2 4
METHOD for solving Homogenous differential equations
dx
duxu
dx
dy
uxy
xduudxdy
Substitute
Substitute
OR
vyx
ydvvdydx dy
dvyv
dy
dx
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Chapter 2 5
Using substitution the homogeneous differential equation
is reduce to separable variable form.Example:2 Solve the homogenous differential
equation
xy
yx
dx
dy 22
Solution:Rewriting in the form : 0,, dyyxNdxyxM
.
022 xydydxyxuxy xduudxdy substitute and
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Chapter 2 6
02222 xduudxuxdxuxx0322222 duuxdxxudxuxdxx
032 duuxdxx
duuxdxx 32
udux
dxx
3
2
udux
dx is variable separable form
udxx
dx cu
x 2
ln2
cx
yx
2
2
2
1ln is general solution.
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Chapter 2 7
Note. Selection of substitution Differential Equation depends on
number of terms of coefficients yxandyxM ,N ,
01321 dydx uxy 1.
If
, then take
2.
If 03211 dydx , then take x vx
3.
If 02121 dydx , then take
x = vy or y = ux
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Chapter 2 8
Example:. Solve the Differential Equation by using appropriate substitution
0222 dyxdxxxyy Solution: Differential equation is homogeneous as degree of each term is same, hence we can use either y = ux or x = vy as substitution
xduudxdy
uxy
Let
Substituting y and dy in the given equation
duxudxxdxxdxuxdxxu
xduudxxdxxuxxu322222
22222
duxdxux
duxdxxdxxu322
3222
1
(1 / 2)
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Chapter 2 9
.tanln
tanln
1
1
1
2
cx
yx
cux
u
du
x
dx
21 u
du
x
dx
is Separable form
Integrating both the sides
is general solution of the differential equation
Separating variable u and x (2 / 2)H
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Chapter 2 10
Example: Show that differential equation
22 943 yxdx
dyxy is homogeneous
dxyxxydy 22 943Solution:
xdvudxdyuxy ,
2 2 2
2 2 3 2 2 2
3 . 4 9
3 3 4 9
x ux udx xdu x u x dx
x u dx ux du x dx u x dx
dxuxdxxudxxduux 222223 64643
(1 / 2)
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Chapter 2 11
x
dx
u
udu
264
3
x
dx
u
udu264
3
ududz
uz
12
64 2
Let
x
dx
z
dz
4
1
.ln64l4
1
lnln4
1
2
2
cxx
yn
cxz
is general solution of the differential equation
is Separable form
Integrating both the sides
(2 / 2)
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Chapter 2 12
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Chapter 2 13
(1 / 3)
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Chapter 2 14
(2 / 3)
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Chapter 2 15
(3 / 3)H
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Chapter 2 16
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Chapter 2 17
(1 / 2)
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Chapter 2 18is general solution of differential equation
(2 / 2)H
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Chapter 2 19
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Chapter 2 20
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Chapter 2 21
is general solution of differential equation
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