微積分学 II 演習問題

 II

II 1 2

1

II 2

6

II 3

10

II 4

16

II 5

19

II 6 2

23

II 7

28

II 8

33

II 9

40

II 10

42

II 11

47

II 12 3

52

II 13

57

II 14

63

II 15

72

II 1 2

1. , .

cos(xy)

(1) lim

(

x y

)(

2 1

)

1 + 2xy

x3 - 3xy

(4)

(

x y

lim )(

0 0

)

x2

+

y2

x4 + 2y4

(7) lim

(

x y

)(

0 0

)

x2 + y2

xy

(10)

lim

(

x y

)(

0 0

)

x4

+

y2

ex2+y2 - 1

(13) lim

(

x y

)(

0 0

)

x2 + y2

x2y2

(16)

lim

(

x y

)(

0 0

)

x2

+

y4

ey sin(xy)

(2) lim

(

x y

)(

0 0

)

xy

2x3 - y3

(5)

lim

(

x y

)(

0 0

)

4x2

+

y2

x3 + y4

(8)

lim

(

x y

)(

0 0

)

x2

+

4y2

xy3

(11)

(

x y

lim )(

0 0

)

x2

+

y4

sin xy

(14)

(

x y

lim )(

0 0

)

x2

+

y2

(17) lim xy

(

x y

)(

0 0

)

x2 + y2

x2 - y2

(3)

lim

(

x y

)(

0 0

)

x2

+

y2

xy2

(6)

lim

(

x y

)(

0 0

)

x2

+

y4

x2 - 2y2

(9)

lim

(

x y

)(

0 0

)

3x2

+

y2

(12) lim xy sin 1

(

x y

)(

0 0

)

x2 + y2

1 - cos x2 + y2

(15) lim

(

x y

)(

0 0

)

x2 + y2

(18) lim (x2 + y2) log(x2 + y2)

(

x y

)(

0 0

)

2. (n) (n = 3, 4, . . . , 18) , R2 fn . (

,

f3

f3

(

x y

)

=

x2 - y2 x2 + y2

.)

f?n

: R2

R

f?n

(

x y

)

=

fn 0

(

x y

)

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

, n = 3, 4, . . . , 18 , f?n .

3. () (1) R2 f?2

ey sin(xy)

f?2

(

x y

)

=

ey

xy

xy = 0 xy = 0

,

{ (

x y

)

R2

xy

=

} 0

f?2

.

(2) R2 f?1

cos(xy)

1 xy = -

f?1

(

x y

)

=

1

+

2xy

2 1 xy = -

2

2

,

{ (

x y

)

R2

xy

=

-

1 2

}

f?1

.

1

1

1.

(1)

f

:

{

(

x y

)

R2

xy

=

}

-

1 2

( -,

)

-

1 2

(

-

1 2

,

) ,

g

:

( -,

)

-

1 2

(

-

1 2

,

)

R

(f

(

x y

)

=

xy,

g()t)

=

cos(t) 1 + 2t

,

f,

g

,

lim

(

x y

)(

2 1

)

cos(xy) 1 + 2xy

=

lim g(f

(

x y

)(

2 1

)

(

x y

))

=

g

(

x y

lim )(

2 1

)

f

(

x y

)

=

g(f

(

2 1

))

=

g(2)

=

1 .

5

sin t

(2)

f

:

R2

R,

g

:

R

R

f

(

x y

)

=

xy,

g(t)

=

t

1

t = 0 , f t=0

, lim g(t) = lim sin t

t0

t0 t

(

)

= 1 = g(0) , g 0 .

lim sin(xy)

(

x y

)(

0 0

)

xy

=

lim g(f

(

x y

)(

0 0

)

(

x y

))

=

g

(

x y

lim )(

0 0

)

f

(

x y

)

= g(0) = 1 ,

lim

ey sin(xy) =

lim

ey

lim

sin(xy) = 1.

(

x y

)(

0 0

)

xy

(

x y

)(

0 0

)

(

x y

)(

0 0

)

xy

(3)

x2 - y2

(

x y

lim )(

0 0

)

x2

+

y2

,

c

,

f

: R2

R

x2-y2

f

(

x y

)

=

x2 +y 2

c

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

, f

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

,

lim f (g(t))

t0

=

f

(

0 0

)

=

c

.

,

k

,

g

g(t)

=

(t, kt)

,

t2 - k2t2

lim

t0

f

(g(t))

=

lim

t0

t2

+

k2t2

=

1 - k2 1 + k2

,

lim f (g(t))

t0

lim

t0

g(t)

=

(

0 0

)

g

c

.

,

x2 - y2

(

x y

lim )(

0 0

)

x2

+

y2

.

(4)

x3 - 3xy

lim

(

x y

)(

0 0

)

x2 + y2

,

c

,

f

: R2

R

x3-3xy

f

(

x y

)

=

x2 +y 2

c

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

, f

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

,

lim f (g(t))

t0

=

f

(

0 0

)

=

c

.

,

k

,

g

g(t)

=

(t, kt)

,

lim f (g(t))

t0

=

lim

t0

t3 - 3kt2 t2 + k2t2

t - 3k

=

lim

t0

1

+

k2

=

-3k 1 + k2

,

lim f (g(t))

t0

lim

t0

g(t)

=

(

0 0

)

g

c

.

,

(

x y

lim )(

0 0

)

x3 x2

- +

xy y2

.

(5) x2 4x2 + y2, y2 4x2 + y2 , |2x3| 2|x|(4x2 + y2), |y3| |y|(4x2 + y2) . |2x3 - y3|

|2x3|

+

|y3|

(2|x|

+

|y|)(4x2

+

y2)

,

(

x y

)

=

(

0 0

)

2x3 - y3 4x2 + y2

2|x| + |y| . ,

(

x y

)

(

0 0

)

,

2|x|

+ |y|

0

,

,

lim

(

x y

)(

0 0

)

2x3 4x2

- y3 + y2

=

0

.

(6)

xy2

(

x y

lim )(

0 0

)

x2

+

y4

,

c

,

f

: R2

R

xy2

f

(

x y

)

=

x2 +y 4

c

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

, f

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

lim f (g(t))

t0

=

f

(

0 0

)

=

c

.

,

k

,

g

g(t)

=

(kt2, t)

,

lim f (g(t))

t0

=

kt4

lim

t0

k2t4

+

t4

=

k k2 + 1

,

lim f (g(t))

t0

lim g(t) =

t0

(

0 0

)

g

c

.

,

xy2

(

x y

lim )(

0 0

)

x2

+

y4

.

2

(7) lim

(

x y

)( 00

)

x4 + 2y4 x2 + y2

,

c

,

f

: R2

R

x4+2y4

f

(

x y

)

=

c

x2 +y 2

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

,

f

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

,

lim f (g(t)) t0

=

f

(

0 0

)

=c

.

,

k

,

g

g(t)

=

(t, kt)

, lim f (g(t)) = lim

t0

t0

t4 + 2k4t4 t2 + k2t2 =

1 + 2k4 1 + k2

, lim f (g(t)) t0

lim g(t) =

t0

(

0 0

)

g

c . , lim

(

x y

)(

0 0

)

x4 + 2y4 x2 + y2

.

(8) x2 x2 + 4y2, y2 x2 + 4y2 , |x3| |x|(x2 + 4y2), |y4| y2(x2 + 4y2) . |x3 + y4|

|x3|

+ |y4 |

(|x| + y2 )(x2

+ 4y2 )

,

(

x y

)

=

(

0 0

)

x3 + y4 x2 + 4y2

|x| + y2

.

,

(

x y

)

(

0 0

)

,

|x| + y2

0

,

,

lim

(

x y

)(

0 0

)

x3 + y4 x2 + 4y2

=

0

.

(9)

x2 - 2y2

(

x y

lim )(

0 0

)

3x2

+

y2

,

c

,

f

: R2

R

x2-2y2

f

(

x y

)

=

3x2 +y 2

c

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

,

g

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

,

lim f (g(t))

t0

=

f

(

0 0

)

=

c

.

,

k

,

g

g(t)

=

(t, kt)

,

t2 - 2k2t2

lim

t0

f (g(t))

=

lim

t0

3t2

+

k2t2

=

1 - 2k2 3 + k2

,

lim f (g(t))

t0

lim

t0

g(t)

=

(

0 0

)

g

(10)

(cxy)lim( 00)x4x+yy2 .,(,xy)lim( 00)3xx2 2c-+2yy22 , f: R2.

R

xy

f

(

x y

)

=

x4 +y 2

c

(

x y

)

=

(

0 0

)

(

x y

)

=

(

0 0

)

, f

(

0 0

)

.

,

lim g(t)

t0

=

(

0 0

)

g

:

R

R2

,

lim f (g(t))

t0

=

f

(

0 0

)

=

c

.

,

k

,

g

g(t)

=

(t, kt3)

, lim

t0

kt4

k

f (g(t)) =

lim

t0

t4

+ k2t6

=

lim

t0

1 + k2t2

c . ,

= k , lim f (g(t)) lim g(t)

xty0

(

x y

lim )(

0 0

)

x4

+

y2

t0

.

=

(

0 0

)

g

(11)

()

()

x2 + y4 2

x2y4

=

|x|y2.

(

x y

)

=

(

0 0

)

|x|y2 x2 + y4

1 2

,

2xy3 x2 + y4

|y| 2

.

,

(

x y

)

(

0 0

)

,

|y|

0

,

,

lim

(

x y

)(

0 0

)

xy3 x2 + y4

=

0

.

(12)

sin 1 x2 + y2

1 xy sin 1 x2 + y2

|xy|

.

,

(

x y

)

(

0 0

)

,

|xy|

0

,

, lim xy sin 1

= 0 .

(

x y

)(

0 0

)

x2 + y2

et-1

(13)

f

:

R2

R,

g

:

R

R

f

(

x y

)

=

x2

+

y2,

g(t)

=

1

t

t = 0 , f t=0

,

lim g(t)

t0

=

lim

t0

et

-1 t

=

1

=

g(0)

,

g

0

.

lim

(

x y

)(

0 0

)

ex2+y2 - 1 x2 + y2

=

lim g(f

(

x y

)(

0 0

)

(

x y

))

=

3

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