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四则运算【教学目标】运让学生充分掌握四则混合运算的计算方法,并且应用到题目当中。方法概念1.四个优先(1)若不能简便运算,优先将小数化为分数;(2)优先将带分数化为假分数;(3)优先将百分数化为分数;(4)优先将除号化为乘号;2.格式与步骤要
求:(1)必须有“解:原式=”字样;(2)建议步骤写成四步,即:统一格式、去掉小括号、去掉中括号、求出结果。3.演草要求:单独准备演草本,演草本要像写作业。四则运算之繁分数运算4.先将“大分数线”变为除号,并用“四个优先”统一形式;按照混合运算的要求解题。四
则运算之逆运算5.“剥洋葱法”口诀:由外往里,层层剥离;6.“倒算法”口诀:分子变为“1”,两边同时倒;7.“借来还去法”口诀:有借有还,莫忘记还。例1)]785.37(41[5−例2]5.4)32234.3(1033[57−+例321172115)
75.0322(1741+−例48553161)613321(625.0−++例554)]6151213(32[−+例62175.152.026.0433211例731564512158121
10.9742-4+例8]65212)322211[(]4)911312(75.0[−+−−例9求等式()1061.951581-21332-6.5=+中的代表的数。例10已知54372
61−−−x=45079,求x。例11已知983]3)21(75.052[12=+++。求?基础演练1)5.0]283)2175[(15+−2)1124)48.1751(111296.273
3)312]71)10941211(5.13[−+4)513]651)75.2323(542[−+巩固提升1)75%3111.252110-9.62)))]41(2.1[(]731)51225[(%%−+3)已知:220943.0513.531--532=
+,求出的值。4)8.132152]1011)2851(322[547=−−+。求?1.)]4.0101231155.5(3[5.25−−%2.3529)2112541187(24−−+3.]31265)322211[(81−+4
.)25.06.304153()]5448.5(199.1[+−+%5.))]41(2.1[(]731)51225[(%%−+6.已知1184112111=+++x,求x。1、)]785.37(41[1
0−\2]5.4)32234.3(1033[34−+3)]4.0101231155.5(3[51−−%41136)48.1751(111296.2765、109)]6151213(32[−+6217352.026.04332117
75%3111.252110-9.68]65212)322211[(]4)911312(875.0[−+−−9求等式()1061.951581-21332-6.5=+中的代表的数。10已
知:220943.0513.531--532=+,求出的值。参考答案例1)]785.37(41[5−3203454353415====例2]5.4)
32234.3(1033[57−+633140633100571006335710030310335713100101103357293002021033572930080010021033572930080033341033572938100334103357==
=+=+=+=−+=−+=−+=)()()()()()(例321172115)75.0322(1741+−6814631220917211217732172
145938172123143381721172123143381721==+=+=+−=+−=)()()(例48553161)613321(625.0−++5.2482529548252402925482560002962585856162962
5.0=−=−=−=−+=例554)]6151213(32[−+5.14556456110732==−+=例62175.152.026.04332114115415==例73156451215812110.9742-4
+25.164315451078643151045786431551110237204643155111523239107184===+−=+−=例8]65212)322211[(]4)
911312(75.0[−+−−158569465359465526166941911436552382341910-3743==−=−+−=−+
−=)()()(例9求等式()1061.951581-21332-6.5=+中的代表的数。)05.55-9.695.612069295.61295.6169323295.61233311
095.612315351095.612315726351095.61231572646391095.6123157232213为负数()()()()()()()()(解:=+=+=+−=+−=+−=+−=+−
−=+−−例10已知5437261−−−x=45079,求x。6.154541255431279754312795437245437792450679543779245054377926794507
95437261==−=−−=−=−−=−−−=−−=−−−=−−−解:例11已知983]3)21(75.052[12=+++。求?4.85256230258015303258
23610325832214352863322143529833221435212===++=++=++=++=+++解:基础演练8
5.05.75.02155.032814315.1=+=+=+=1114648.1127231196.273.2==23776377122722737712511227.3==−=−+=)()(323316510
33165215141651161211514165116411311514.4==+=+=−+=)()(2.14.86.94334542216
.9.5=−=−=巩固提高2.14.86.94334542216.9.1=−=−=8.25427547102049120967105114196.02.171051141.2===+=
+=)()()(5.85164926372126154212651321522126513220892061172313513.3===−=−=−−=−−=+−−)(:812161516135316
13103910113161321011316135395951101131613539592315210118161338539.4===+=+=−+=−+=−−+=
−−+)(3.085.0%5.2515.23%5.2525.54.73%5.25251021485.13%5.25.1==−=−−=−−=))()(352935
2429242935241039242935125813242935125868724293521125458724.2==−=−=−+=−−+=)()()()()(3138813
7581375662581375661669813756382381.3==−=−=−+=−+=)()()(1.06.83409.
246.83119.09.146.30453119.09.1.4==+=++=)()(8.25427547102049120967105114196.02.171051141.5===+=
+=)()()(25.1108668856961187126811868141111814681111181144211111841412111.6==+=+=++=+++=+++=+++=+++3403410431034110
.1====189940063310034100633341003031033341310010110333429300202103334293008001002103334293008003334103334
2938100334103334.2===+=+=+=−+=−+=−+=)()()()()()(
6.085.0%5115.23%5125.54.73%51251021485.13%51.3==−=−−=−−=))()(5.1116948.1127231196.276.4==34910569106110732.5=
=−+=8130415.6==2.14.86.94334542216.9.7=−=−=60415672416535724165526166941911876552382341910-3787.8==−=−+−=
−+−=)()()()05.55-9.695.612069295.61295.6169323295.61233311095.612315351095.612315726351095.61231572646391095.6
123157232213.9为负数()()()()()()()()(解:=+=+=+−=+−=+−=+−=+−−=+−−5.851
64926372126154212651321522126513220892061172313513.10===−=−=−−=−−=+−−)(解: