问题 解答题
(难应用举例)已知向量
AB
=(2-k,-1)
AC
=(1,k)

(1)若△ABC为直角三角形,求k值;
(2)若△ABC为等腰直角三角形,求k值.
答案

(1)

AB
=(2-k,-1),
AC
=(1,k)⇒
BC
=
AC
-
AB
=(k-1,k+1)

①若∠A=90°,则

AB
AC
(2-k,-1)•(1,k)=0,∴k=1;

②若∠B=90°,则

AB
BC
(2-k,-1)•(k-1,k+1)=0,得k2-2k+3=0无解;

③若∠C=90°,则

AC
BC
(1,k)•(k-1,k+1)=0,得k2+2k-1=0,

k=-1±

2

综上所述,当k=1时,△ABC是以A为直角顶点的直角三角形;

k=-1±

2
时,△ABC是以C为直角顶点的直角三角形.

(2)①当k=1时,

AB
=(1,-1),
AC
=(1,1)⇒
|
AB
|
=|
AC
|=
2

②当k=-1+

2
时,
AC
=(1,-1+
2
)
BC
=(-2+
2
2
)

|

AC
|=
4-2
2
|
BC
|=
8-4
2
|
AC
|≠
|
BC
|

③当k=-1-

2
时,
AC
=(1,-1-
2
)
BC
=(-2-
2
2
)

|

AC
|=
4+2
2
|
BC
|=
8+4
2
|
AC
|≠
|
BC
|

综上所述,当k=1时,△ABC是以BC为斜边的等腰直角三角形.

阅读理解

阅读理解。

     Jee Hock and Meng Kim were very good friends. Jee Hock could not see. He was blind. Meng Kim could

not walk. He was lame. They lived in a village near a forest. Everyone in the village was going to a rich man's

dinner on the other side of the forest. Jee Hock and Meng Kim were anxious to attend the dinner too.

     Blind Jee Hock thought of a plan. He would carry Meng Kim. The lame man could tell him the way. Meng

Kim said that the plan was a good one.

     On the way through the forest, Meng Kim saw a tiger. He did not tell Jee Hock about is. Instead, he quietly

asked Jee Hock to carry him to the mearest tree. Upon reaching an over banging branch, Meng Kim quickly

hauled himself up.

     Then the tiger roared. Jee Hock at once knew a tiger was near. He lay down quietly. The tiger came to him

and sniffed his body. The tiger's whiskers touched Jee Hock's nose. At once Jee Hock sneezed,

"Ah choooooo!"The tiger was afraid and ran away.

     Then Meng Kim came down from the tree. He asked Jee Hock about the tiger. Jee Hock said that the tiger

had told him to choose his friends wisely.

1. Jee Hock and Meng Kim were good _____.

A. men

B. tigers

C. friends

D. brothers

2. They decided to go to _____.

A. a picnic

B. a dinner

C. a party

D. the cinema

3. When Meng Kim saw the tiger, he _____.

A. shouted loudly

B. did not tell Jee Hock about it

C. quickly climbed up a tree

D. lay down quietly

4. Jee Hock sneezed because the tiger's whiskers _____.

A. hurt him

B. was very long

C. cut his nose

D. touched his nose

判断题