20比几多了25

有点做不到.希望网友们!是第31题. 31.2012.重庆市 下图为物质的分类关系①与②是并列关系③包含在②中若②是纯净物则③不可能是   A. 已知x>y>0且xy=1.求x2+y2/x-y的最小值及此时xy的值 x+y=1,则x2+y2+xy得最小值为x,y＞0 已知x, y>0,求(1-x)(1-y)(1+xy)/(1+x2)(1+y2)的最小值x2表示x的平方,“/”左边所有的是分子,右边所有的是分母,请写出尽可能详细的解答过程,谢谢!高二理科数学题，提示：三角换元，设x=tanα∈R，然 一道化学题,解答过程,思路,要写清楚 若x不等于0是x2+xy-2y2=0,则x2+3xy+y2/x2+y2=急!详细!10分钟哦! 已知x不等于,x2-x=3,y2-y=3,求x2-xy+y2的值注意哦,是x2-xy+y2求值.（可以用韦达定理,学过的） 1、实验测得CO,N2,和O2等三种气体体积的混合气体的密度是H2的14.5倍,其中O2的质量分数是多少?若其中CO和N2物质的量之比为1:1,则混合气体中氧元素的质量分数是多少?2、H2和CO2混合气体在同温同 某菜农原计划每亩菜地施用氮肥硫酸铵〖（NH4）2 SO4 〗13.5kg,后来在科技人员的指导下,打算改施用尿素〖CO（NH2）2）〗.如果要达到同样的施肥效果,则每亩菜地需施尿素为? "伤脑筋"用英语怎么说? 几个比较伤脑筋的英语题目．1．My brother likes swimming .I like swimming,too.〔改为同义句〕2.Zhao peng is __[good] at math than Liu Hai.[注：be good at是固定搭配,能否将good转换成比较级better.] 3.The children all ov 取镁粉,铝粉,铁粉,锌粉组成的混合物17.2克,跟一定量的稀硫酸恰好完全反应.经蒸干水后,得到固体成物60.4(不含结晶水).求生成氢气多少克?这是一道初三的题 45678 计算36g水（H2O）中氢元素和氧元素质量的质量分别是多少? 已知0小于等于x小于等于1 若x2+y2=3,xy=1,则x-y= 但为何不可以是1 为了测定食盐中的钙元素含量取10g食盐溶于水、加入足量盐酸、生成0.011mg二氧化碳、计算此加钙食盐中钙元素的质量分数 【英语】高中英语选择题（ ） it is to go outing for a picnic in spring!A.How funB.How funnyC.What great funD.What a great fun-------------------------------------------------------------------------------------------参考答案是C, 已知X等于-2,Y等于2分之1求 （XY)100次方的值 若（x+2）的2次方+|y+2分之1|,则（xy）的2007次方等于（ ） 第八题, 已知x加y等于4 xy等于1 求x的5次方y的4次方加x的4次方y的5次方 x+y=-5,xy=3,则x的2次方+y的2次方等于 He can earn _______________ 100 dollars a month.A.as many as B.as many as 设X,Y为实数,求X方加2XY加2Y方减4Y加5的最小值并求出此时XY的值 when you answer question in a job interview ,please remerber the golden rule-----always give the monkey ____ he wantsA.what B.that为什么不能选B另外这是一个什么句型？为什么that不能是做he wants的宾语呢 Mom,shall I play computer games?No,________.A I'd rather not.B I'd rather you not.C I'd rather you didn'tD I'd like not to. some seemingly harmless clogs night become harmful when on the internet by millions of people .A to read B reading C read D being read 该选择哪个?求解释求说明,还有,那个打错了，是blogs，改正阿，记得阿 实数xy满足x^2+y^2+2x-4y+1=0,求下列各式的最大最小值（1）y/（x-4） （2）2x-y我想知道为什么y/（x-4） =(y-0)/(x-4),可理解为圆上点（x,y)到（4,0）点斜率的范围 题目我大都会做,希望有高手能详细解释下每道题选择这个答案的原因及相关语法点,以及其他选项的错误之处：答得好的还有加分1.it's quite obvious that the aging population in china will cause_______ heavy 1.What should Iwear for the English speaking composition?Dress------ you like.A.which B.that C.however D.whenever2.Yellow Mountain is such an attractive place of interest ------ everyone likes to visit.A.as B.that C.which D.whenever3.---------,Franks He took us on a tour__B__the place where he was born and raised.A.to B.of C.towards D.over为什么呢To most foreigners,a rising China is__B__an opportunity____a threat.A.other;than B.more;than C.better;than D.rather;than请问more...than、rather.. 1.The lawyer wasn't injured in the car accident because she ____ a seat belt.A.has on B.put on C.wore D.dressed.说说选C,不选ABD的理由2.All changes of matter ____ changes in the form of the energy.A.involve B.contain C.are made of D.inclued说