Write the correct words according to the commands. 按要求写单词。

1. hot (反义词)                           2. thirteen (序数词)                    

3. no (同音词)                            4. meat (同音词)                        

5. nine (序数词)                          6. is (过去式)                             

7. sun (形容词)                           8. twelve (序数词)                      

利用配方法证明代数式-10x²+7x-4的值恒小于0．由上述结论，你能否写出三个二次三项式，其值恒大于0，且二次项系数分别是l、2、3？