小学数学课件(1) 23页

循环小数江阴市城南小学徐敏\n你听过这样的故事吗？从前有座山，山上有座庙，庙里住个老和尚，老和尚对小和尚说，从前有座山，山上有座庙，庙里住个老和尚，老和尚对小和尚说，从前有座山，山上有座庙，庙里住个老和尚，老和尚对小和尚说……\n1.请同学们分组计算这些题，看哪个组做的又对又快。0.75÷2.5   32÷6   2.7÷11\n)3265.3330201820182)2.7110.24545225044605550446055532÷6 =5.33……2.7÷11 =0.24545……例7.例8.讨论：综合上面32÷6  2.7÷11商的情况，观察商的小数部分和余数有什么关系？\n)3265.3330201820182)2.7110.24545225044605550446055532÷6 =5.33……2.7÷11 =0.24545……例7.例8.\n)3265.3330201820182)2.7110.24545225044605550446055532÷6 =5.33……2.7÷11 =0.24545……例7.例8.\n)3265.3330201820182)2.7110.24545225044605550446055532÷6 =5.33……2.7÷11 =0.24545……例7.例8.\n.5.35.33······写作循环小数的写法0.24545······5.03070307······写作写作0.2455.0307..6.2121······写作3.163861861······写作..\n.5.35.33······写作循环小数的写法0.24545······5.03070307······写作写作0.2455.0307....6.21..6.2121······写作3.163861861······写作\n.5.35.33······写作循环小数的写法0.24545······5.03070307······写作写作0.2455.0307....6.21....3.1638616.2121······写作3.163861861······写作\n.5.35.33······写作循环小数的写法0.24545······5.03070307······写作写作0.2455.0307....6.21..5.745=..3.1638616.2121······写作3.163861861······写作..5.745745······\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······4.6.\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······2.142857..4.6.\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······2.142857..4.6.\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······2.142857..4.6.3.331.06254.66······2.142857142857······2.384615······6.17582······有限小数无限小数\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······2.142857..4.6.3.331.06254.66······2.142857142857······2.384615······6.17582······有限小数无限小数\n练习：下面各数中的商哪些是循环小数，循环小数用简便写法写出。（1）0.666÷0.2=3.33（2）17÷16=1.0625（3）1.4÷0.3=4.66······（4）15÷7=2.142857142857······（5）3.1÷1.3=2.384615······（6）5.62÷0.91=6.17582······2.142857..4.6.3.331.06254.66······2.142857142857······2.384615······6.17582······有限小数无限小数\n判断(1)循环小数是无限小数。()(2)无限小数是循环小数。()×√\n对于循环小数，也可以根据实际需要，取它的近似数0.245（保留两位小数）0.245（保留三位小数）....≈0.25≈0.245\n对于循环小数，也可以根据实际需要，取它的近似数0.245（保留两位小数）0.245（保留三位小数）....≈0.25≈0.2450.245=..0.24545······\n精确到个位精确到十分位精确到百分位精确到千分位..用“四舍五入法”写出下表中各循环小数的近似数4.8907.275..54.94.894.89177.37.287.275\n课外拓展如果用A、B、C表示不同的三个数字，如：A.BBCBBC······可以简写成什么数？这个小数的小数部分第一百位是什么？