- •Module 3
- •Topic 1 .Differential equations of the first order and the first degree
- •Typical problems
- •Self-test and class assignments
- •Individual tasks
- •1.1. Solve the separable differential equations.
- •1.2. Solve the homogeneous differential equations.
- •1.3. Solve the linear differential equations.
- •1.4. Solve the Bernoulli’s differential equations.
- •1.5. Find the general solution and also the particular solution through the point written opposite the equation.
- •1.6. Solve the exact differential equations.
- •Various types of differential equations with appropriate substitution will be considered in the following articles (see table 3.1).
- •Table 3.1
- •Consider other types of differential equations with appropriate substitution for reduction of order:
- •1) a differential equation
- •Typical problems
- •Self-tests and class assignments
- •Answers
- •Table3.2
- •Table 3.4
- •Examples of typical problems
- •Class and self assignments
- •Answers.
- •3.2. Find the general solutions of linear homogeneous equations.
- •3.3. Find general the solutions of linear homogeneous equations with right part of special form.
- •3.4. Solve Cauchy’s test for equations of the second order.
- •3.5. Solve the equations using the Lagrange’s method.
- •Examples of typical problems solving
- •Tests for general and self-studying
- •Answers
Particular, that solution |
y =C |
is proceeded from the general solution, |
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if C1 =0 . |
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4. Solve |
y¢¢¢-(y¢¢)2 =0 . |
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Solution. An equation is of order 3 and does not contain x and y, directly, |
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and it depends on y . |
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substitution |
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necessary, as follows |
y ¢¢(x) = z(x) or y p( y) . It’s suitable to use |
this |
substitution y ¢¢(x) = z(x) |
.Eventually we would obtain the resultant equation in the form of First order, as follows; z ¢-z2 = 0 .
Then we have:
dxdz = z2 , dzz2 = dx , -1z = x +C1 , z = -x -1 C1 , y ¢¢ = -x -1 C1 ,
y ¢ = ò -x -1 C1 dx =-ln x +C1 +C2 ,
y = ò (-ln x +C1 +C2 )dx =-(x +C1 ) ln x +C1 +C2 x +C3 –
Is the general solution of the given equation ( C1 , C2 , C3 –constants)
T 2. Self-tests and class assignments
Evaluate the following equations: |
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1. |
y |
1x . |
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2. |
y 27e3x |
120x3 . |
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3. |
y e5x cos x . |
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4. |
y sin 2x cos x . |
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5. |
y e x |
x . |
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6. |
y x2 |
cos3x . |
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7.. |
y ln x x . |
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8. |
y 5x |
6x . |
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9. |
y 3x |
cos x . |
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10. y 4 x |
cos 3x sin 5x . |
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2 |
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y |
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xy |
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1 . |
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12. |
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y |
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0 . |
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y |
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13. (1 x2 )y xy 2 . |
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14. |
y |
5y . |
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15. |
y |
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2 |
y |
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16. |
y |
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2e |
y |
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1 y y |
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17. |
y |
3 |
y |
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1. |
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18. |
yy |
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(y ) |
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