XAỰC ỦŨNH A ỦEỒ TỬỨ A(0,A) KEỶ ỦỬỤÙC 2 TIEỎP TUYEỎN ỦEỎN(C) SAO CHO 2 TIEỎP ỦIEỒM ỦEỎN NAỐM VEÀ 2 PHỚA CUỶA 0X
2) Xaực ủũnh a ủeồ tửứ A(0,a) keỷ ủửụùc 2 tieỏp tuyeỏn ủeỏn
(C)
sao cho 2 tieỏp ủieồm ủeỏn naốm veà 2 phớa cuỷa 0x.
0
2
y
x
0
0
1
( ;
) ( )
x
M x y
0 0
C
Goùi
Phửụng trỡnh tieỏp tuyeỏn cuỷa (C) taùi M:
'( )(
)
y
f x
x x
y
0
0
0
2
2
4
2
x
x
x
3
(
)
0
3
0
0
y
x x
y
x
2
0
1
2
2
x
x
x
x
(
0
1)
0
(
0
1)
(
0
1)
2 4
2
x
x
0
0
a
x
(
1)
2
a
x
a
x
a
(
1)
2
2(
2)
2 0
0
(1)
Tieỏp tuyeỏn qua A(0,a)
(vỡ
x
0
=1 khoõng laứ nghieọm)
a
a
1 0
1
,
0
2
a
Khi ủoự (1) coự 2 nghieọm laứ
ẹieàu kieọn ủeồ coự 2 tieỏp tuyeỏn keỷ tửứ A laứ:
x
0
,
x
1
1
2
1
1
1
vaứ
ẹieàu kieọn 2 tieỏp ủieồm naốm veà 2 phớa
Tung ủoọ tieỏp ủieồm
Ox.
2
2
2(
) 4
x
x
x x
x
x
0
1
0 1
0
1
0
.
0
0
y y
x
x
x x
x
x
0 1
0
1
1
1
0 1
0
1
1
2 4(
2)
4
9
6
2
a
a
a
a
a
1
1
0
0
3
2 0
2 2(
2)
1
3
3
1
1