题目

第二节短文改错（每小题1.5分共15分） When I walked into the classroom, the teacher was handing in the tests. I was feeling very nervous. I had not studied      76. _____________ at all at the weekend as I had thought it would be easy test.         77. _____________ I went through the test for many times but I could only answer    78. _____________ three out from the twenty questions. I did not want to fail   79. _____________ the exam. Then, I put my book under my desk, opening it      80. _____________ and started looking for the answer. The teacher wasn小刚同学动手剪了如图①所示的正方形与长方形纸片若干张．观察与操作：（1）他拼成如图②所示的正方形，根据四个小纸片的面积之和等于大正方形的面积，得到：a2+2ab+b2=（a+b）2，验证了完全平方公式；即：多项式  a2+2ab+b2 分解因式后，其结果表示正方形的长（a+b）与宽（a+b）两个整式的积．（2）当他拼成如图③所示的矩形，由面积相等又得到：a2+3ab+2b2=（a+2b）（a+b），即：多项式 a2+3ab+2b2 分解因式后，其结果表示矩形的长（a+2b）与宽（a+b）两个整式的积．问题解决：（1）请你依照小刚的方法，利用拼图分解因式：a2+4ab+3b2．（画图说明，并写出其结果）（2）试猜想面积是2a2+5ab+3b2的矩形，其长与宽分别是多少？（画图说明，并写出其结果）