mathematics 2
DESCRIPTION
question of mathematics 2TRANSCRIPT
1
BWM 12303
Tutorial 2 1. Solve
(a) 21
dy xdx y
=+
(b) 12
dy ydx x
+=+
(c) ( )3 21 dyx x ydx
+ = (d) x y dye xdx
+ =
(e) 2 2dy dyx xy ydx dx
− = − (f) 2cos 2 tandyy x xdx
= +
(g) ( )2 1dy x ydx
= − (h) 22 1x dye y ydx
− = + −
(i) 5 10, (0) 0dI I Idt
+ = = (j) 2sec , ( ) 0dyx x ydx
π= =
2. Determine whether the functions given below are homogeneous or not.
(a) 2
3 3( , ) xyf x yx y
=+
(b) 2
2
2 3( , )2
xy yf x yx xy
+=+
3. Solve
(a) 2dy x y
dx x−= (b) 2 2 2dyx x xy y
dx= − +
(c) 2 22 4dyxy y xdx
= + (d) 22 3
2dy xy ydx xy
+=
(e) 2 3dyx y xdx
= + (f) , (1) 1dy y x ydx y x
−= =+
(g) ( )3 3 2 0dyx y xydx
+ − = (h) 2 2 2 0dyx y xydx
− − =
(i) ( ) ( )2 2x y dy xy dx+ = (j) 2 3 33 4 , (1) 2dyxy y x ydx
= − =
4. Solve the following linear differential equations.
(a) dyx x ydx
= + (b) 2 3dyx y xdx
= +
(c) 2dy xy xdx
+ = (d) 2 , (2) 1dyx y x ydx
+ = =
(e) xdy y edx
− = (f) xdyx y edx
+ =
2
(g) cot cosdy y x xdx
+ = (h) cot dyx x ydx
= +
(i) 3xdy xe ydx
−= − (j) 3
2
( 1)( 1) 21
dy xx ydx x
++ = +−
(k) 2
12 , (1) 11
dyx y ydx x
⎛ ⎞= − =⎜ ⎟+⎝ ⎠ (l)
lndy yxdx x x
= −
5. Show that the following differential equations are exact. (a) (2 3 ) (2 3 ) 0x y dx y x dy+ + + = (b) 2(2 cos ) ( sin ) 0x xye x dy e y y x dx− −+ − − =
(c) 3 2 21 14 6xy dx x y dyx y x y
⎛ ⎞ ⎛ ⎞+ = − +⎜ ⎟ ⎜ ⎟+ +⎝ ⎠ ⎝ ⎠
(d) sinsin
xy
xy
dy ye y xydx xe x xy
−= −−
6. Solve the following differential equations.
(a) 2
4 32
2 4 2 0x xy dx xy dyy y
⎛ ⎞⎛ ⎞+ + − + =⎜ ⎟⎜ ⎟
⎝ ⎠ ⎝ ⎠
(b) ( ) ( )3 2 2 2 36 2 2 9 4 4 0xy x y dx x y xy y dy+ + + + + =
(c) ( ) ( )2 22 cos sin 0y ye xy x dx xe x dy+ + + =
(d) ( ) ( )2 cos cos sin 0x y x y x yxe e y xy dx xe xy xy xy dy+ + ++ + + + + =
(e) ( ) ( )2 2cos 1 cos 2 2y ye y xy dx x xy xe dy− + = − −
(f) ( ) ( )( )1 2 0xe y x y dx x y dy+ + + + =
(g) 2 2
2 2 18 , (1) 1y xx dx dy yy x y x
⎛ ⎞ ⎛ ⎞+ + = + =⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
(h) 2
1 2 ln 1 01 ( 1)
y xdx x dyx y y
⎛ ⎞ ⎛ ⎞+ + + − + =⎜ ⎟ ⎜ ⎟+ +⎝ ⎠ ⎝ ⎠
7. A glass of lemonade with a temperature of 1000F is placed in a refrigerator with
constant temperature of 700F, and 1 hour later its temperature is 88.20F. Find the time when the temperature is 750F. What does the value of the temperature approaches if the time approaches infinity?
8. Cooling off a body from 1000C to 800C takes 5 minutes. If the room temperature is
260C, how long will it take to reach 300C?
3
Solutions
1. (a) 2
2
2y y x C+ = + (b) (2 ) 1y C x= + −
(c) ( )1
3 31y C x= + (d) y x xe xe e C− −= − − +
(e) 2ln 2lny y x C− = − + (f) 2 24 tan tany x x C= + +
(g) 21ln1
y x Cy− = ++
(h) 1 2 1ln3 1
xy e Cy− = ++
(i) ( )52 1 tI e−= − (j) 2 sin 2 cos 2siny x x x x x C= + − +
2. (a) Homogeneous function (b) Homogeneous function
3. (a) 21 Ay xx
⎛ ⎞= −⎜ ⎟⎝ ⎠ (b) 11
lny x
Ax⎛ ⎞
= −⎜ ⎟⎜ ⎟⎝ ⎠
(c) ( )2 2 2 4y x Ax= − (d) 12 2y x Ax
⎛ ⎞= −⎜ ⎟
⎝ ⎠
(e) 2 3y Ax x= − (f) 2 2
1ln tan ln2 4
y x y xx
π−⎛ ⎞+ ⎛ ⎞+ = − +⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠
(g) 3 33 lny x Ax= (h) 2 213
Ay xx
⎛ ⎞= −⎜ ⎟⎝ ⎠
(i) 2
2 ln2x Ayy
= (j) 3 4 37y x x= +
4. (a) lny x x Cx= + (b) 23y x Cx= − +
(c) 21
2xy Ce−= + (d)
2y xx
= −
(e) x xy xe Ce= + (f) xe Cyx+=
(g) 1 sin csc2
y x C x= + (h) tan secy x x C x= − + +
(i) 31 12 4
x x xy xe e Ce− − −= − + (j) 2 21 1( 1) ln ( 1)2 1
xy x C xx
+= + + +−
(k) 2
2
1 1ln 12xy
x⎛ ⎞+= +⎜ ⎟⎝ ⎠
(l) 2 21 1 12 ln 4
y x C xx⎛ ⎞= + −⎜ ⎟⎝ ⎠
4
5. (a) 3M Ny x
∂ ∂= =∂ ∂
(b) 2 sinxM N ye xy x
−∂ ∂= = − −∂ ∂
(c) 22
112( )
M N xyy x x y
∂ ∂= = −∂ ∂ +
(d)
cos sinxy xyM N xye e xy xy xyy x
∂ ∂= = + − −∂ ∂
6. (a) 2
4 2xxy y Cy
+ + = (b) 2 3 2 23 ( )x y x y C+ + =
(c) 2sinyxe y x C+ = (d) sinx yxe y xy C+ + = (e) 2 sin 2yxe xy y x C− + + = (f) 2x xxye y e C+ =
(g) 22 4 5x y xy x− + = (h) ln 2
1xy x x y Cy
+ + + =+
7. 0.5( ) 70 30 tT t e−= + , 3.5835 hrst = , 700F.
8. 0.063( ) 26 74 , 46.31 minutestT t e t−= + = .