- •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
The constant С is defined from the initial condition: 50 20 100 C , thus С=500.
Consequently, v 20t 2 500 . Finally, the speed of the particle after 2 min from rest is
v = 20 1202 +500 = 288500 10 2885 (m/seс).
T1. Self-test and class assignments
Solve the separable differential equations.
1. |
|
xydx (x 1)dy 0 . |
2. |
xydx (1 y 2 ) |
1 x 2 dy 0 . |
||||
3. |
|
y 5 y . |
4. |
y y 2 1 . |
|
||||
5. |
|
x 2 ( y 3 5)dx (x3 5) y 2 dy 0 . |
6. y 33x 2 y . |
|
|||||
7. |
|
4yy tg x(4 y 4 ) . |
8. 1 y 2 dx 1 x 2 dy 0 |
||||||
9 |
* |
. |
y |
|
3x 4 y . |
|
* |
|
|
|
|
10 . |
y ( y x) 1 . |
|
Find the general solution and also the particular solution through the point written opposite it.
11. yxy e y 0 , y(1) 0 .
12.tg ydx x ln xdy 0 , x e .
2
13.cos 2 x sin 2 ydy sin x cos 2 ydx 0 , x(0) 0 . Solve the homogeneous differential equations.
|
|
|
|
|
x2 y 2 |
|
|
|
|
|
|
|
2 |
|
|
|
|
|
2 |
|
|
y |
|
||
14. |
y |
|
|
|
0 . |
15. |
xydy y |
dx (x y) |
e |
x |
dx . |
||||||||||||||
xy |
|
|
|
||||||||||||||||||||||
|
|
|
|
|
|||||||||||||||||||||
16. |
(x 2 y)dx xdy 0 . |
17. |
xy |
¢- y = x tg |
y |
. |
|
|
|
|
|
||||||||||||||
|
|
|
|
|
|
||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
x |
|
|
|
|
|
|
18. |
(x y)dx ( y x)dy 0 . |
19. (x2 xy)dy y2dx 0 . |
|
|
|
||||||||||||||||||||
|
|
|
|
|
|
y |
|
|
|
|
|
|
y |
|
|
|
y |
|
|
|
|
|
|
||
20. |
|
|
|
|
|
|
21. |
|
|
|
x |
|
|
|
|
|
|
|
|||||||
xy |
x sin x |
y . |
y |
e |
x 1 . |
|
|
|
|
|
|||||||||||||||
|
|
|
|
|
|
|
|
|
Transform the given equations into homogeneous ones and solve them.
203
22. |
y |
2x y 1 |
23. |
y |
x 2 y 3 |
||
|
. |
|
. |
||||
x 2 y 3 |
2x 4 y 1 |
24.(x y)dx (2 y x 1)dy 0 .
25.(x y 1)dx (2y 2x 1)dy 0 .
Solve the linear differential equations of the first order.
26. |
y y e x . |
|
|
|
|
27. |
y 2xy 1 2x 2 . |
|
|
||||||||
28. |
xy y x2 |
3x 2 . |
|
|
29. tdx (x t sin t)dt 0 . |
||||||||||||
30. |
2y dx |
x |
2 y3 . |
|
|
31. |
y ¢+ y cos x =sin x cos x . |
||||||||||
|
|
|
dy |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
32. |
y 4 y cos x . |
|
|
33. |
y ¢+ y tg x = cos2 x . |
|
|
||||||||||
34. |
y |
2 |
y e x (x 2) . |
|
|
35. |
y ¢- y ctg x = 2x -x2 ctg x . |
||||||||||
x |
|
|
|||||||||||||||
|
|
|
|
|
|
x |
|
|
|
|
|
|
|
|
|
||
Solve the Bernoulli’s differential equations. |
|
|
|
|
|||||||||||||
36. |
xy 2 y x 2 y 3 . |
37. y ¢ = y4 cos x + y tg x . |
|
|
|||||||||||||
38. |
|
|
|
|
|
2x y |
39. |
|
+x |
2 |
|
¢ |
|
2 |
|
||
|
|
|
|
|
|
|
|
|
|
|
|||||||
xy |
2y cos2 x . |
(1 |
|
) y |
-2xy = 4 (1+x |
|
) y arctg x . |
||||||||||
|
|
|
|
Solve the exact differential equations.
40.2xydx (x 2 y 2 )dy 0 .
41.(2xy 3y 2 )dx (x 2 6xy 3y 2 )dy 0 .
42.(x sin y)dx (x cos y sin y)dy 0 .
43.(x2 y2 y)dx (2xy x e y )dy 0 .
44.(3x 2 y sin x)dx (x3 cos y)dy 0 .
|
|
2 |
|
|
x3 |
|
45. |
3x |
|
(1 ln y)dx |
2 y |
|
dy . |
|
|
|||||
|
|
|
|
|
y |
|
|
|
|
|
|
|
Compose and solve the differential equations.
46.Radium decomposes at a rate proportional to the amount present. If of 100 mg. set aside now there will be left 98,3 mg. 50 years hence, find how much will be left t centuries from the time when the radium was set aside and also how long a time will elapse before one tenth of the radium has disappeared.
47.Find the equation of all curves which cut the circles x2 + y2 = R2 16 at an angle of 450.
204
48.Find the equation of the curve such that each of its tangent lines together with the coordinate axes encloses a constant area equal to 9.
49.The force exerted by a spring is proportional to the amount the spring is stretched and is 10 kg when the spring is stretched 2 cm. A 10 kg weight is hung on the spring and is drawn down slowly until the spring is stretched 4 cm and then released. Find the equation, the period, the amplitude, and the frequency of the resulting motion.
Answers
|
|
|
|
|
|
1. y C(x 1)e x , x 1 . |
|
2. 1 x 2 ln |
|
|
y |
|
|
|
y 2 |
|
C . |
|
|
|
3. |
2 |
|
|
y x C . |
|
|||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||||||||||||||||
|
1 |
|
|
|
|
|
1 y |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2 |
|
|
|
|
|
|
|
|
|
|
5 |
|
|
|
|
|
|
|
|
|
|||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||||||||||||
4. |
ln |
x C . |
5. ( y 3 5)(x3 |
5) C . 6. |
3 3 2 y 2 33x |
C . |
7. |
arctg y2 = |
|
||||||||||||||||||||||||||||||||||||||||||
|
|
1 y |
|
||||||||||||||||||||||||||||||||||||||||||||||||
2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||
= ln |
|
cos x |
|
+C . |
8. |
arcsin x +arcsin y = C . 9*. |
y Ce4x |
3 |
x |
3 |
|
. |
Hint. Use the |
||||||||||||||||||||||||||||||||||||||
|
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
4y 3x z(x) . |
10*. |
|
|
|
|
|
|
|
|
|
|
|
|
|
4 |
|
|
16 |
|
|
|
|
|
|
|
|
|
|
|
|||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||||||||||||
substitution |
y ln |
|
x y 1 |
|
C . |
Hint. Use |
the |
substitution |
|||||||||||||||||||||||||||||||||||||||||||
y x z(x) . 11. x 2 1 2e y ( y 1) . 12. x esin y . 13. tg y y |
|
1 |
|
|
|
1 . |
|
|
|
|
|
||||||||||||||||||||||||||||||||||||||||
cos x |
|
|
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||
14. x2 (x2 2y2 ) C . |
|
|
|
|
|
|
|
|
|
|
y |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||||||||||
15. (x y) ln Cx xe x . |
16. y = (Cx -1)x, x = 0 . |
||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
y |
= ln(C x2 + y2 ) . |
|
|
|
|
|
|
|
|
|
y |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||||
17. y x arcsin(Cx) . |
18. arctg |
19. y Ce x . |
20. y = 2xarctgCx . |
|
|||||||||||||||||||||||||||||||||||||||||||||||
x |
|
||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
y |
|
|
|
|
|
Cx |
|
22. x2 |
xy 3y x y 2 C . |
|
|
|
|
|
23. x2 |
4y 2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||||||||||||||
21. e x |
|
|
|
|
. |
|
|
|
|
|
4xy 6x 2y C . |
||||||||||||||||||||||||||||||||||||||||
1 |
|
|
|
|
|
|
|||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
Cx |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||||
24. |
x 2 |
y |
2 |
xy |
y C . |
25. x 2y 3ln |
|
x y 2 |
|
C . |
|
|
|
|
|
26. y Ce |
x |
|
1 |
e |
x |
. |
|||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|||||||||||||||||||||||||||||||||||||||||||||
2 |
|
|
|
|
|
|
|
|
|
|
2 |
|
|||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
27. y Ce x2 x . |
28. y |
c |
|
x 2 |
|
3x |
|||
x |
|
2 |
|||||||
|
|
|
|
|
3 |
|
|||
+ |
2 |
y3 . 31. y Ce sin x |
sin x 1 . |
|
|||||
|
|
||||||||
7 |
|
|
|
|
|
|
|
|
|
y C cos x sin x cos x . |
|
34. y Cx 2 |
|||||||
37. y-3 = (C -3tg x)cos3 x, |
y = 0 . |
|
2 . |
29. x |
c |
sin t cos t . |
30. x = |
|
c |
+ |
|||||||||
|
|
t |
|
|
t |
|
|
|
|
y |
||||||
32. y Ce4x |
|
1 |
(sin x 4 cos x) . |
33. |
||||||||||||
17 |
||||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
e x . |
35. y C sin x x 2 . 36. |
y3 Cx3 |
3x 2 . |
|||||||||||||
|
38. |
|
|
|
|
y = tg x + |
C +ln |
|
cos x |
|
|
. |
||||
|
|
|
|
|
|
|
||||||||||
|
|
|
|
|
x |
|
|
|
|
|
||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
205