题干

已知3是一元二次方程x2﹣2x+a=0的一个根,求a的值和方程的另一根.

上一题 下一题 0.0难度 选择题 更新时间:2013-07-08 10:56:50

答案(点此获取答案解析)

解:将x=3代入x2﹣2x+a=0中得32﹣6+a=0,

解得a=﹣3,

将a=﹣3代入x2﹣2x+a=0中得:x2﹣2x﹣3=0,

解得x1=3,x2=﹣1,

所以a=﹣3,方程的另一根为﹣1.

同类题3

阅读下面这篇文章,完成下列各题。

妈妈和房客

美国凯•福布斯

    ①妈妈在窗外贴出“租房启事”,海德先生应租而来。这是我们家第一次出租房屋,所以妈妈忽略了弄清海德先生的背景和人品,也忘了让他预付房费。

    ②“房子我很满意,”海德先生说,“今晚我就送行李来,还有我的书。”他顺顺当当地住进了我家。平时,他好像没有固定的工作时间,常和善地与我家的孩子逗趣。当他走过我妈妈坐着的大厅时,总是礼貌地弯弯腰。我爸爸也喜欢他。爸爸喜好回忆迁居美国前住过的挪威。海德去过挪威,他能与爸爸起劲地聊在那儿钓鱼的野趣。

    ③只有开客栈的杰妮大婶不欣赏我们的房客。她问:“他什么时候交房租呢?”“向人要钱总难开口,他会很快付清的。”妈妈答道。但杰妮大婶只是了两声,“这种人我以前见得多了,别指望借给人一件新外套,回来还是好的。”妈妈笑笑:“兴许你说得对。”她递上一杯咖啡,止住了杰妮大婶的嘟囔。

    ④雷雨天里,妈妈担心海德的屋子夜里冷,就让爸爸邀请他到暖和的厨房和我们一起坐。我的两个姐姐、哥哥尼尔斯、还有我在灯下做作业,爸爸和海德靠着炉子叨着烟斗,妈妈在洗盘子或是在小桌上静静地工作。

    ⑤海德能辅导尼尔斯的高中课程,有时还帮他学拉丁文。尼尔斯渐渐对学习产生了兴趣,他不再求爸爸让他停学做工了。当我们做完了作业,妈妈坐在摇椅上拿起针线时,海德就给我们讲他的旅游奇遇。噢,他知道的可真多。那些美妙的历史和地理,便随他走入我们的屋子和生活。

    ⑥有天晚上,他给我们读狄更斯的书,很快,读书成了我们生活的一部分。我们写好作业,海德就夹一本书来高声朗读,一个神奇的新世界向我们洞开。

    ⑦妈妈也像我们孩子一样爱听古挪威侠士传奇:“太好听了!”海德还朗读莎士比亚的戏剧。他悦耳的男低音,听起来像是大演员。即使在天气暖和的晚上,我们也不再出去玩耍。妈妈对此很欣慰。她是不喜欢我们天黑上街的。而最值得高兴的,还是尼尔斯几乎不再混到街头的野孩子堆里。有天晚上,孩子们在街上闯了祸,而尼尔斯正和我们一起听《孤星血泪》的最后一章。

    ⑧就在我们急于听完一个骑士的传奇时,一封信送到了海德手里。第二天一早,他告诉妈妈要离开。“我得走了,”他说,“我把这些书留给尼尔斯和其他孩子。这是一张我所欠房租的支票。夫人,对您的好心款待,我深表谢意。”我们再也不能听他读完那个故事了。

    ⑨我们伤感地看着海德先生离开了,同时,又为能在厨房继续读书感到兴奋。那么多的书啊!妈妈精心地整理了书堆:“我们可以从这里学到很多东西。尼尔斯能代替海德先生读书,他也有一副好嗓子。”我看得出来,这使尼尔斯很自豪。

    ⑩就在这一天,妈妈向杰妮大婶亮出海德的支票:“你看,收回的还是一件好外套。”

    ⑪几天后,开面包铺的克瑞波先生来我家,怒气冲天地喊道:“那个海德是个骗子,瞧他给我的支票,全是假货。银行的人告诉我,他早把款兑光了。”在一旁的杰妮大婶得意地点着头,那神态分明是说:“看,我不是提醒过你们了吗?你们不听嘛。”“我敢打赌,他也欠了你们家许多钱,是不是?”克瑞波不无希望地探问道。

    ⑫妈妈转过身向着我们,目光长久地停留在尼尔斯身上,然后走到炉子边,把支票投入炉火。

    ⑬“不!”他向克瑞波先生回答道,“不,他什么也不欠。”

(选自《世界微型小说名家名作百年经典》有改动)

同类题4

阅读理解

    The bike-sharing companies that are powering a transportation revolution in China's urban centers are not like those in the rest of the world. Their bikes have no docking ports or assigned zones for parking. Instead, riders open their smartphone apps, hop on, and start riding. So easy!

    In 2015, Ofo, China's bike-share pioneer, launched its first fleet of bicycles in Beijing. The bikes' bright yellow frames were soon met by the orange-rimmed(镶边), basket-equipped models launched by Mobike, Ofo's main competitor today. In little over a year, the two companies have had a huge impact on revitalizing (重振) cycling in China, particularly among young people.

    Ofo placed 1 million bicycles across 35 cities and registered 15 million users in its first years, while Mobike has now gained more than 10 million unique users and bicycles in 21 cities. Inspired by their success, at least 10 other companies have jumped into the market, launching their own app-powered, brightly colored bikes in quick succession. But Mobike and Ofo are far ahead of them.

    The two industry leaders each take a different marketing method to a similar product. The Mobike app uses GPS to display bikes' locations to users. They can use the map to reserve a bike and walk over to it. A scan of the bike's QR code (二维码) unlocks the bike, and when users manually(手动地) lock the bike at the end of their trip, the app records the trip's end and the bike will pop back up on the map as available. Equipped with this wireless technology, Mobikes cost between 1,000 and 3,000 yuan. Rides cost 1 yuan for an hour or a half hour, depending on whether a user chooses a “Lite” or regular bike, and the deposit (押金) required to the service is 299 yuan.

    Ofo, meanwhile, is devoted not just to producing its own bikes, which have slim yellow bodies and cost about 250 yuan, but also to connecting existing bikes to its network----- a philosophy that begins with the practice of 2000 bikes offered to a campus bike-share program. The 2000 bikes were the first generation of Ofo. Yet the majority of the company's bikes are currently ones that have been specially manufactured and fitted with their lock system. Unlike Mobike,Ofo bikes themselves are offline: their locations are tracked through users' cell phones. Users find a free bike, enter the license plate number into their app, and receive the bike unlock code. When they have reached their destination, they end the ride on the app and manually lock the bike. Rides cost 1 yuan for an hour and the deposit is 99 yuan.