题干

在△ABC中,内角A、B、C所对的边分别是a、b、c,已知3asinC=ccosA.

(Ⅰ)求sinA的值;
(Ⅱ)若B=
π
4
,△ABC的面积为9,求a的值.
上一题 下一题 0.0难度 选择题 更新时间:2019-12-03 08:38:16

答案(点此获取答案解析)

解:(Ⅰ)∵3asinC=ccosA.∴2sinAsinC=sinCcosA,∵sinC≠0,∴tanA=
1
3
,且A为锐角,∴sinA= <

同类题1

阅读下面的文字,完成小题

篆刻之美

孙莉莉

    篆刻艺术在狭小的天地中,依靠笔画的技巧,表现出刚柔相济的笔情刀趣,生动优美的造型图形,古朴隽永的金石气韵,给人以情感意蕴的震动和审美艺术的享受。篆刻的起源,笼罩着某些神秘的气氛,除货赂用玺节说、殷墟铜玺起源说等,最有趣味的应该是龙凤授玺说。从甲骨文的卜辞和陶器上的印纹、刻文来探讨其背后的真相,从中能感受到篆刻印章的社会历史地位及文化艺术气息。唯其如此,我们才能让一个长期悬而不决的问题得到破解。篆刻艺术的成熟期为何来得那么早,正是在皇权至上这种社会效用及信物凭证这种实际价值的双重作用下,促成了篆刻艺术在春秋战国及秦汉之际就十分辉煌绚丽的早熟局面。篆刻从发展开始,就是以“文字”的形式存在的,或者更确切地说是一种特殊的“符号”,经过若干时代的成长,成熟为以文字为主要内容存在的艺术形式,也就是成熟的篆刻艺术。尽管篆刻从唐至宋元曾一度中落,但从明至清,像文彭、何震、黄士陵、吴昌硕等一批有艺术觉悟和创造精神的篆刻家则追踪秦汉,在先民博大的印学宝库中吸纳了丰富的养料,再度汇融于书学画理,从而使篆刻艺术再度振兴,开创了绮丽多姿的流派印。

    篆刻作为一种艺术创作活动,其形式与内涵、价值与效应是积淀在整个文化系统内,活跃在整个社会化过程中的,因而对篆刻艺术的发展产生了综合影响,为篆刻艺术的更新和突破提供能量和契机。如春秋战国玺印的瑰丽奇妙,千姿百态,正是“百家争鸣”时代精神在印面上的折射。又如汉相官印的浑朴持重、沉雄老健,将军印的刚劲豪壮、气势酣畅,体现了雍容大度的相官之风和豪放英武的将军之气。从这个意义上讲,篆刻是一种综合艺术,一种文化现象,一种美学系统。篆刻不是技术操作,工匠制作,而是艺术创作,才情的显现。

(选自《论中国传统浮雕与篆刻艺术的关系》)

同类题2

阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中选出可以填入空白处的最佳选项。

    No doubt we all have experienced frustration(受挫). It may be something as 1 as growing flowers or as serious as developing better relationships with others. Whatever the 2 is, there comes a point when you just feel you can't go on any further.

     And yet, the secret to 3 can be found in a tube of toothpaste. Every time I come to the 4 of a tube of a toothpaste, I am completely 5 that just when I think it is absolutely empty, I can 6more toothpaste out of it. I am sure you all have gone through the 7 thing.

    So, next time you find yourself in such a situation, 8 the tube. We can all 9times that success came when we were on our 10 chance or when we were doing something for the final time. It is when you dig deep down for that one last burst of 11 that you achieve your goal.

    12 , too many people give up too early. All they 13 to do is squeeze one more drop of toothpaste from the tube. There are hundreds of 14 of successful people who kept on going in the face of adversity(逆境) and 15. Even the writers of Chicken Soup for the Soul were 16 by 33 publishers before they found one who would 17their book.

    If you have the passion to go for your 18, then keep squeezing that “inner tube of toothpaste”. It is only when you 19 the “passion” that you will know whether success is yours or not. Just make sure that you don't 20 too soon. Success may be just around the corner.

同类题3

根据短文理解,选择正确答案。

    Some unwelcome visitors from North America have been turning up in the waters off the coast of Great Britain.

    North American lobsters (龙虾) have been found in the North Sea (between Great Britain and Northwest Europe), far from their own habitat. The lobsters usually live along the eastern coast of Canada and the United States.

    It is impossible that the lobsters could have made the 5,600-kilometre journey on their own. They were probably brought to Britain and then got away from containers. Some of the lobsters that were caught had elastic bands (松紧带) holding their legs shut, like lobsters that are kept in containers in stores or restaurants.

    Many may have been “set free” from some ships passing through the area. Sometimes passengers order a live lobster from a tank in the dining room and then ask the waiter to throw it overboard instead of cooking it.

    According to official records, 26 North American lobsters have been caught in waters off Great Britain since 1988. However, it is believed many more have been found but not reported.

    It is against the law to let North American lobsters come into British waters. If they settle down in European waters, it would be bad for the local lobsters. The two live in the same place and eat the same food. But North American lobsters are larger, stronger and more aggressive (好斗的) than European lobsters, and they produce young more quickly.

    As a result, they could take food and space away from the local lobsters, and from other types of shellfish that live in the same area. These lobsters may also carry diseases that could harm the local lobsters.