陪孩儿玩数学?四上第11课时　用计算器探索规律
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课本第27页例2，第30～31页练习三第13～14题。
会用计算器计算，再探索计算的规律。
例2，用计算器进行大数的运算，同时探索计算的规律。把计算和探索规律有机地结合在一起，既让孩子学习了用计算器计算的方法，又激发了孩子探索数学奥妙的兴趣，还是培养孩子观察、推理能力的直接途径。
例2，读题，再读算式99。
机算，998。问孩子有什么发现？2×9＝18，得数的首位和末位分别是1和8；相当于把上式的1个9分解为1和8。所以1和8之间有3个9。
机算，997。孩子可能主动说：3×9＝37，1个9分解为2和7，中间还有3个9。
让孩子先猜测996，再用机算验证。进一步验证了上述规律。
探索规律，要让孩子经历“猜测DD验证DD再验证DD运用”的学习过程。
让孩子运用规律直接写出得数。
99×7，9999×9。
补充：99×8。
让孩子用机算进行检验。
也可认为：
99＝1万－1，998＝2万－2，
997＝3万－3，996＝4万－4，
所以，9999×n＝n万－n。
万－5＝4×6＝6万－6＝59994，……。
再整体观察，积的万位从0到8、个位从9到1。让孩子学会欣赏其数学美。
“做一做”。让孩子经历规律的“发现DD验证DD运用”的过程。
先机算前两题，108÷9＝12，3，观察前3题的得数：1，12，123；观察被除数：9＝8＋1，9＝7＋1＋1。n个1，商是n＋1位。
可让孩子把算式抄写到本子上，并做到各个算式之间数位、除号、除数、等号对齐。写得数时，数字对齐，即1和1对齐，2和2对齐。
观察11106÷9，被除数9＝6＋1＋1＋1，商是4位数，得数可能是1234，用机算验证。
运用规律直接其余式题写出得数。再用计算器检验。
最后，让孩子在算式的外边画3条直线，所有的算组成了一个等腰三角形。
第13题，让孩子边机算边猜测、验证规律，用前3题总结规律，剩下的习题运用规律。
第一组算式的规律：把142857在右边重写一次，并编上序号，如下：
从编号的数字开始写6位数，便是它对应的乘数和142857相乘的积。如＝的第一个循环节，这组数其实与除数是7的循环节有密切关系。
第三组的算式还可以继续写到9个1乘9个1。整算式也可以画出一个等腰三角形。
第14题，有规律的计算题。先读加法算式，有的孩子可能直接用500×7＝3500进行口算，有的孩子可能用计算器计算。计算后进行比较，让孩子观察计算结果、发现规律，同时突出用简便方法计算可能比计算器还要快。
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+999+99+9的简便算法是怎样算的?具体点儿!
9+1+999+1+99+1+9+1-5==111105Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
I've been using this piece of code I've written and it's working in this most unclear manner. I wish to insert a row into the database which includes two columns of DateTime:
myrow.ApprovalDate = DateTime.Now
myrow.ProposedDate = DateTime.Now
And yet, when I update the database I receive this error:
SqlDateTime overflow. Must be between 1/1/:00 AM and 12/31/:59 PM.
I've even tried copying an inserted value from the database and hard code it into the object being updated:
// I copied this value from the DB
myrow.ApprovalDate =
Convert.ToDateTime(" 00:00:00.000");
Still same error, the strange part is that the above trick worked for the first insert to the DB but failed from there on. Any ideas what's going on?
86.3k58292382
A DateTime in C# is a value type, not a reference type, and therefore cannot be null. It can however be the constant DateTime.MinValue which is outside the range of Sql Servers DATETIME data type.
Value types are guaranteed to always have a (default) value (of zero) without always needing to be explicitly set (in this case DateTime.MinValue).
Conclusion is you probably have an unset DateTime value that you are trying to pass to the database.
DateTime.MinValue = 1/1/:00 AM
DateTime.MaxValue = 23:59:59.9999999, December 31, 9999,
exactly one 100-nanosecond tick
before 00:00:00, January 1, 10000
Regarding Sql Server
Date and time data from January 1, 1753 through December 31, 9999, to an accuracy of one three-hundredth of a second (equivalent to 3.33 milliseconds or 0.00333 seconds). Values are rounded to increments of .000, .003, or .007 seconds
smalldatetime
Date and time data from January 1, 1900, through June 6, 2079, with accuracy to the minute. smalldatetime values with 29.998 seconds or lower are rounded down t values with 29.999 seconds or higher are rounded up to the nearest minute.
Lastly, if you find yourself passing a C# DateTime as a string to sql, you need to format it as follows to retain maximum precision and to prevent sql server from throwing a similar error.
string sqlTimeAsString = myDateTime.ToString("yyyy-MM-ddTHH:mm:ss.fff")
11.5k32044
I find using the following works quite well for SQL min/max dates after many DB related errors:
DateTime rngMin = (DateTime)System.Data.SqlTypes.SqlDateTime.MinV
DateTime rngMax = (DateTime)System.Data.SqlTypes.SqlDateTime.MaxV
12.4k73765
The code you have for the two columns looks ok.
Look for any other datetime columns on that mapping class.
Also, enable logging on the datacontext to see the query and parameters.
dc.Log = Console.O
DateTime is initialized to c#'s 0 - which is .
This is transmitted by linqtosql to the database via sql string literal : ''.
Sql cannot parse a T-Sql datetime from this date.
There's a couple ways to deal with this:
Make sure you initialize all date times with a value that SQL can handle (such as Sql's 0 :
Make sure any date times that may occasionally be omitted are nullable datetimes
57.8k1082128
Beware when comparing a .Net DateTime to SqlDateTime.MinValue or MaxValue. For example, the following will throw an exception:
DateTime dte = new DateTime();
if (dte &= SqlDateTime.MinValue)
//do something
The reason is that MinValue returns a SqlDateTime, not a DateTime. So .Net tries to convert dte to a SqlDateTime for comparison and because it's outside the acceptable SqlDateTime range it throws the exception.
One solution to this is to compare your DateTime to SqlDateTime.MinValue.Value.
1,38211417
Sometimes in order to write less code it is used to have SQL server set fields like date, time and ID on insert by setting the default value for fields to GETDATE() or NEWID().
In such cases Auto Generated Value property of those fields in entity classes should be set to true.
This way you do not need to set values in code (preventing energy consumption!!!) and never see that exception.
That usually means a null is being posted to the query instead of your desired value, you might try to run the SQL Profiler to see exactly what is getting passed to SQL Server from linq.
6,14711528
This error occurs if you trying to set variable of type DateTime to null. Declare the variable as nullable, i.e. DateTime? . This will solve the problem.
I am seeing the same thing.
The error does not happen on insert of a row but on an update.
the table I am referencing has two DateTime columns neither of which are nullable.
I have gotten the scenario down to getting the row and immediately saving it (no data changes).
The get works fine but the update fails.
We are using NHibernate 3.3.1.4000
Usually this kind of error comes when you do DateTime conversion or parsing. Check the calendar setting in the server where the application is hosted, mainly the time zone and short date format, and ensure it's set to the right time zone for the location. Hope this would resolve the issue.
4,42642871
If u r using NHibernate ORM check ur Datetime files be
Nullable and in ur NHibernate Map Files there are set to nullable.
I had That problem and tryed many time to check all the codes and finaly find it.
DateTime.MinValue and DateTime.MaxValue
DateTime.MinValue = 1/1/:00 AM
DateTime.MaxValue = 23:59:59.9999999, December 31, 9999,
exactly one 100-nanosecond tick
before 00:00:00, January 1, 10000
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Stack Overflow works best with JavaScript enabled计算算式9×12,9×17,9999×19结果有何规律?_百度作业帮
计算算式9×12,9×17,9999×19结果有何规律?
计算算式9×12,9×17,9999×19结果有何规律?
9999×11 = (10000 - 1) * 11 = 110000 - 11 = 1099899999×12 = (10000 - 1) * 12 = 120000 - 12 = 119988.9999×17 = (10000 - 1) * 17 = 170000 - 17 = 1699839999×19 = 189981
首先看989,988,987由这三个算式它结果变化的只有个位上的数和万位上的数，并且当第二个因数的各位为1时积的个位为9、万位为0.当第二个因数的个位为2时积的个位为8、万位为1。由此可以得出积的个位与第二个因数的个位相加为10与积的万位相加为9其余的数不变。9999*（10+A）=1B998C（其中C+A=10，C+B=9）...