1.老树的叹息作文怎么写有没有问题的限制？我觉得，如果你有跟树或者过去的值得叹息的回忆相关的可以写你的真实经历，要是没有的话，就编一个故事吧 。
比如说，你养了一只猫，你和猫之间发生了很多故事，但是后来猫的寿命到了，它离开了你 。树可以再开篇点一下，描述出一个情景，在结尾在点一下，可以是你在树下想猫，风吹过，好像是叹息 。
或者说，猫走了之后，你有时候路过窗口，看到风吹落叶，好像是树的心思 。树和猫之间的联系还是比较容易的，可以写猫在树影斑驳中探出头，在树枝上跳什么的 。
嗯，我写的比较啰嗦，不好意思 。这个是我现在想的，肯定不周到，你写吧 。
2.∫sec^3xdx你好，我来帮你做下：
∫sex^3xdx-∫secxdx=∫（1+tan^2x）secxdx-∫secxdx
【tanxi怎么写】=∫secxdx+tan^2xsecxdx-∫secxdx
=∫secxdx+tanxdsrc^2x-∫secxdx
=∫secxdx+secxtanx-secxdtanx-∫secxdx
=1/2∫secxdx+1/2secxtanx-∫secxdx
=1/2secxtanx-1/2∫secxdx
=sinx/2cos^2x-1/2lnIsecx+tanxI+C
其实这道题并不难，关键在于这个1/2是哪来的？其实是靠“回头积分”得来的，如果能看出这一步，就迎刃而解了！
打得我手都累了，你看看吧，有什么不懂得再问！
3.求证任意7个实数中必存在两个实数x,y,满足0<=(x由于函数y=tanx （-π/2<x<；π/2） 上的值域为R
不妨设这7个数为 tanx1,tanx2, 。,tanx7
对应-π/2=<x1=<x2=< 。=<x7<；π/2
于是根据抽屉原理，必存在xi和xj (i>j，且i,j取自1,2 。,7)
使得0=<xi-xj<；π/6(=<；为“小于等于”)
于是，0=<tan(xi-xj)=(tanxi-tanxj)/(1+tanxi*tanxj)=(yi-yj)/(1+yi*yj)<；√3/3
得证，关键那个表达形式很容易让人想到正切函数
4.急1. "Peter Pan Peter Pan" Du HouganReading the "Peter Pan Peter Pan" This famous work, I benefited from, I know that every child will grow up in this truth.Many children do not want to grow up and do not want to go to school, just want to play every day. Peter Pan is the hero of the book, he is a always the boys do not want to grow up. He never lived in this rural paradise like the same place, where there is such as the bell sounds as beautiful fairy, a mermaid hair, Zhang Buda children, mystery, like the Indians, ferocious pirates and will issue a "ticking "Voice of the crocodile. However, the rich and colorful life, but not a substitute for the mother's desire to Peter. Thus, an equally do not want to grow up, the girls never went to the rural based, on the children when the "mother." They never started in the various rural singular adventure. However, the final text still choose Beattie grew up. She took the children from Nashan mother has for her to fly back to open the windows in the home. And that is always reluctant to grow up the boys, Peter, even though the world can have a happy, but can not enjoy from the warmth of a family. He can only be separated by windows, secretly Zhang Wang window within the stove, a smiling face and kinship. And then quietly walked away, and fairies to disappear in the night sky.Yes ah! Although the township never happy, it does not have the warmth of family, wonderful life. Everyone will grow up and grow into a tree shoring days, as long as our dreams have never townships, and also when they grow up will be very happy and live a more exciting.2. "Wizard of Oz" Du HouganReading the "Wizard of Oz" This novel, I understand the friendliness and mutual assistance among people should unite as one, is not afraid of all the difficulties and move forward the truth.In the main text of more than Lucy gave a young girl aunt and uncle living in the Prairies, one day, the wind suddenly Vol dragon boat suddenly struck, she and her hut, a puppy with Guadao Meng Jin Renqing surprising places. Accidental death of the hut where the evil witch in the East, more than Lucy as a noble woman was magic, and access to the evil Witch of the East Bank of shoes. She very much like to go home, north of good witches guide her to go to the distant country Feicui Cheng Aoci find a magician Aoci help. Lucy has rescued more than the way the brain to find the scarecrow, tin and find the heart to find the courage of a lion…… several in the way they help each other, overcome all difficulties, and the final realization of their own wish.This fairy tale story of breathtaking twists and turns, praised the kindness, courage and the quality of fraternity and mutual help, ideal for the spirit of persistent struggle, is always worthy of our study.3. "Robinson Crusoe" Du HouganReading the "Robinson Crusoe" I know when we are under any circumstances, should believe and respect for their wisdom and courage and the tenacity to overcome self-to overcome the difficulties.This book's main character from childhood who was born in a wealthy family, for their interest in sailing at all to leave their parents, uprooted from their homes, began Chuyang adventure experience. This person's life experience is strange unheard of, and changes in Wanduan his life is unique. But the final text of the hero by virtue of its clever exceptional courage and wisdom to overcome all the world seems difficult to overcome the difficulties.He's such wisdom and courage of our life in all of the things Buwan.看看这些里有没有你中意的 。