问题 填空题

已知实数a,b,c满足a2-2b=-2,b2+6c=7,c2-8a=-31,则a+b+c的值等于 ______.

答案

∵a2-2b=-2,b2+6c=7,c2-8a=-31,

∴a2-2b+b2+6c+c2-8a+26=0,

∴(a-4)2+(b-1)2+(c+3)2=0,

∴a-4=0,b-1=0,c+3=0,

∴a=4,b=1,c=-3,

∴a+b+c=2.

故答案为:2.

单项选择题

I got a job teaching special education at a school in Coachella, California, a desert town about 170 miles from home. It was no (1) job. Street gangs (2) around the school after dark.

"Be careful, " Dad warned me during one of my frequent weekend (3) home. He was concerned about my living (4) , but I needed to be on my own.

One evening, I stayed after school to rearrange my classroom. (5) , I turned out the light and closed the door. Then I (6) toward the gate. It was (7) ! I looked around. Everyone had gone home.

After (8) all the exits, I found just enough (9) to squeeze under a gate in the back of the school. Then I walked toward my car, parked in a field behind the building.Suddenly I heard voices. I (10) around and saw at least eight boys following me. (11) my pace, I reached into my shoulder bag to get my key. I (12) all over the inside of my handbag. But the key wasn’t (13) ! Dear Lord, please help me, I prayed (14) . Suddenly, my fingers touched a loose key in my purse. I didn’t even know if it was for my car, but I took it out and (15) it. It worked!I opened the door, slid in and locked it—just (16) the teenagers surrounded the car. Trembling , I started the engine and (17) away. When I returned to my apartment, the phone was ringing. It was my Dad. I didn’t tell him about my experience; I didn’t want to (18) him. "Oh, I forgot to tell you!" He said, "I had a (n) (19) car key made and slipped it into your purse—just (20) you ever need it. \

14().

A.loudly 

B.nervously 

C.carefully 

D.silently

判断题