已知函数y=x2+2x-1（t≤x≤t+1）
（1）若此函数的最小值为M，求M关于t的函数表达式；
（2）当t为某一正整数n时，求函数值y可以取得的所有正整数的和．
（1）∵y=x2+2x-1=（x+1）2-2，对称轴为x=-1．
∴最小值为M=
；(t+2)2-2．t＜-2 -2．-2≤t≤-1 (t+1)2-2．t＞-1
（2）由（1）对称轴x=-1，
∴得n2+2n-1≤y≤n2+4n+2
∴y可以取得的正整数为n2+2n-1，n2+2n，n2+2n+1，…n2+4n+2．共2n+4个
∴y可以取得的所有正整数的和为
=(n+2)(2n2+6n+1)(2n+4)(2n2+6n+1) 2
=2n3+10n2+13n+2（10分）
| 完形填空。 | |||
| The Dragon Boat Festival is celebrated 1 the fifth day of the fifth lunar month by 2 zongzi and holding dragon boat races. The festival began during the period of Warring States (战国时期), and has a 3 of more than 2,000 years. The date of the festival is said to be the date 4 Qu Yuan died. He was a wise and upright (正直的) man, and was loved 5 people. He wanted the emperor of Chu 6 against the State of Qin with the cooperation (联合) with the State of Qi, 7 was refused and sent to the border area. During his stay in other states, he wrote 8 poems expressing his strong feelings for Chu. On the day when Chu was defeated by Qin, Qu Yuan 9 into Miluo River expressing his strong love for his native land by taking 10 own life. After the 11 of Qu Yuan, people of Chu went to Miluo River to mourn (哀悼) over the great 12 they loved so much. Some threw eggs and rice wrapped in leaves into the river to feed the fish 13 keep them away from Qu Yuan. Some doctors poured realgar wine 14 the river to kill snakes and other animals that might try to eat Qu Yuan. Now the Dragon Boat Festival has become a 15 festival for the Chinese people. | |||
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