已知集合A={x|x2+（b+2）x+b+1=0}={a}，求集合B={x|x2+ax+b=0}的真子集．
∵集合A={x|x2+（b+2）x+b+1=0}={a}，
∴方程x2+（b+2）x+b+1=0有两个等根，∴△=0，
即（b+2）2-4（b+1）=0，∴b=0，
∴x2+（b+2）x+b+1=0即x2+2x+1=0，∴x=-1，
∴集合B={x|x2+ax+b=0}={x|x2-x=0}={0，1}，
集合B的真子集有∅，{1}，{0}．
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| I didn't cry when I leamed I was the parent of a mentally disabled child. When Kristi was old enough to 1 school,we sent her to a kindergarten (幼儿园). During Kristi's second year in school,she faced a very 2 experience. A meeting based on music and PE activities 3 be held in her school. On the day of the program,Kristi 4 to be sick,but I insisted that she should take part in the activities. Just 5 I had forced her to go to school,now I forced myself to go to the 6 . When the performance began,I knew 7 Kristi had been worried. Her class was divided into relay teams. 8 her limp and slow,clumsy reactions (反应) ,she would surely 9 her team. The performance went surprisingly well, 10 , until it was time for the sack race (套袋赛跑). Now each child had io climb into a sack from a standing position,jump into a goal line,return and climb out of the sack. I watched Kristi 11 near the end of her line of players,looking sad. But as Kristi's turn came,a(n) 12 took place in her team. The tallest boy in the line stepped behind Kristi and placed his hands on her waist. Two other boys stood a little ahead of her. 13 the player in front of Kristi stepped from the sack, those two boys grabbed the sack and held it 14 while the tall boy lifted Kristi and 15 her nearly into it. A girl in front of Kristi took her hand and supported her until Kristi 16 her balance.Then 17 she jumped,smiling and proud. Among the 18 of teachers,schoolmates and parents,I crept off by myself to thank God for the 19 , understanding people in life who make it 20 for my disabled daughter to be like her fellow human beings. Then I finally cried. | ||||
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