五年級上冊 人教版 數(shù)學 第一單元《整數(shù)乘法運算定律推廣到小數(shù)》課件

五年級上冊—人教版—數(shù)學—第一單元整數(shù)乘法運算定律推廣到小數(shù)

理解整數(shù)乘法運算定律對于小數(shù)乘法同樣適用，會運用這些運算定律進行小數(shù)乘法的簡便計算。進一步發(fā)展數(shù)感。學習目標一、復(fù)習引入乘法交換律乘法結(jié)合律乘法分配律整數(shù)乘法運算定律a×b=b×a(a×b)×c=a×(b×c)(a+b)×c=a×c+b×cb×a(b×c)a×c+b×c0.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5？？？二、探究新知0.7×1.2=1.2×0.7=0.8×(0.5×0.4)=2.4×0.5＋3.6×0.5=(0.8×0.5)×0.4=（2.4＋3.6)×0.5=二、探究新知小數(shù)四則混合運算的順序跟整數(shù)是一樣的。請同學在練習本上算一算......0.840.840.160.16330.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5二、探究新知0.840.840.160.163======3===從上面的算式中，你發(fā)現(xiàn)了什么規(guī)律？0.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5二、探究新知===乘法交換律乘法結(jié)合律乘法分配律整數(shù)乘法的交換律、結(jié)合律和分配律，是否適用于小數(shù)乘法？1.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.50.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5二、探究新知===1.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.50.7×1.21.2×0.7二、探究新知=1.2×0.74.9×66×4.90.12×0.240.24×0.12==整數(shù)乘法交換律對于小數(shù)乘法也適用。0.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5二、探究新知===1.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.50.8×(0.5×0.4)(0.8×0.5)×0.4二、探究新知=0.8×(0.5×0.4)(0.12×0.4)×0.250.12×(0.4×0.25)二、探究新知(0.12×0.4)×0.250.12×(0.4×0.25)=0.012=0.048×0.25=0.012=0.12×0.10.8×(0.5×0.4)(0.8×0.5)×0.4二、探究新知=0.8×(0.5×0.4)(0.12×0.4)×0.250.12×(0.4×0.25)=你可以再舉出幾個這樣的例子嗎？(0.3×0.6)×0.70.3×(0.6×0.7)=1.25×(0.8×4)(1.25×0.8)×4=整數(shù)乘法結(jié)合律對于小數(shù)乘法也適用。2.4×0.5＋3.6×0.5（2.4＋3.6)×0.5二、探究新知=2.4×0.5＋3.6×0.50.8×(0.125＋0.4)0.8×0.125＋0.8×0.4二、探究新知0.8×(0.125＋0.4)0.8×0.125＋0.8×0.4=0.42=0.8×0.525=0.42=0.1＋0.322.4×0.5＋3.6×0.5（2.4＋3.6)×0.5二、探究新知=2.4×0.5＋3.6×0.50.8×(0.125＋0.4)0.8×0.125＋0.8×0.4=(0.3+0.7)×0.40.3×0.4+0.7×0.40.15×(0.08+0.02)0.15×0.08+0.15×0.02==

整數(shù)乘法分配律對于小數(shù)乘法也適用。0.7×1.21.2×0.70.8×(0.5×0.4)2.4×0.5＋3.6×0.5(0.8×0.5)×0.4（2.4＋3.6)×0.5===整數(shù)乘法的交換律、結(jié)合律和分配律，對于小數(shù)乘法也適用。二、探究新知

根據(jù)運算定律填空。（課本第12頁的第1題）2.5×(0.77×0.4)＝(

×)×4.2×1.69＝×7.2×8.4＋2.8×8.4＝(＋)×1.694.22.50.40.777.22.88.4(乘法交換律）(乘法結(jié)合律）(乘法分配律）想用對運算定律，那要先觀察算式和數(shù)據(jù)特點哦！2.5×0.4=17.2個8.42.8個8.410個8.4+=10個8.4(乘法交換律和乘法結(jié)合律）0.25×4.78×4簡便計算0.65×202二、探究新知0.25×4.78×4（乘法交換律）=0.25×4×4.78=1×4.78=4.78簡便計算0.65×2020.25×4=1二、探究新知0.25×4.78×4（乘法交換律）=0.25×4×4.78=1×4.78=4.780.65×202=0.65×(200＋2)=1301.3=131.3=0.65×200(乘法分配律）（把202改寫為：200+2）＋二、探究新知簡便計算0.65×2＋0.25×4.78×4（乘法交換律）=0.25×4×4.78=1×4.78=4.780.65×202=0.65×(200＋2)=1301.3=131.3=0.65×200＋0.65×2(乘法分配律）＋二、探究新知簡便計算用簡便方法計算下面各題（課本第12頁第2題）請同學們在練習本上寫一寫。三、鞏固練習（2）101×0.45（3）4.75×99＋4.75（1）0.034×0.5×0.6（4）2.73×99=0.034×(0.5×0.6)=0.034×0.3=0.0102=(100+1)×0.45=100×0.45+1×0.45=45+0.45=45.45（乘法結(jié)合律）（乘法分配律）2.用簡便方法計算下面各題（課本第12頁第2題）（2）101×0.45（3）4.75×99＋4.75（1）0.034×0.5×0.6（4）2.73×99=0.034×(0.5×0.6)=0.034×0.3=0.0102=(100+1)×0.45=100×0.45+1×0.45=45+0.45=45.45=(99+1)=100×4.75=47599個4.751個4.75×4.75=2.73×=2.73×100-2.73×1=273-2.73=270.27(100-1)（乘法結(jié)合律）（乘法分配律）（乘法分配律的逆向思維）（乘法分配律）三、鞏固練習2.用簡便方法計算下面各題（課本第12頁第2題）（2）101×0.45（3）4.75×99＋4.75（1）0.034×0.5×0.6（4）2.73×99=0.034×(0.5×0.6)=0.034×0.3=0.0102=(100+1)×0.45=100×0.45+1×0.45=45+0.45=45.45=(99+1)=100×4.75=475×4.75=2.73×=2.73×100-2.73×1=273-2.73=270.27(100-1)（乘法結(jié)合律）（乘法分配律）（乘法分配律的逆向思維）（乘法分配律）四、課堂總結(jié)三、鞏固練習四、課堂總結(jié)1.整數(shù)乘法的交換律、結(jié)合律和分配律，對于小數(shù)乘法也適用。2.在進行簡便計算前，要先觀察算式和數(shù)據(jù)特點，再靈活選擇乘法運算定律計算。3.在應(yīng)用乘法分配律計算時，可靈活使用正向思維和逆向思維。謝謝觀看！五年級上冊—人教版—數(shù)學—第一單元整數(shù)乘法運算定律推廣到小數(shù)（答疑）

在計算下面各題時，小明應(yīng)用了乘法運算定律來計算，請判斷他都做對了嗎？(1)(0.8+8)×125=0.8×125+8=100+8=108(2)(0.4×4)×2.5=0.4×2.5×4×2.5=1×10=10(3)2.8×1.8-0.8×2.8=2.8×(1.8-0.8)×2.8=2.8×1×2.8=7.84(4)2.4×98=2.4×100-2=2.4×100-2=240-2=238提問=0.8×125=100+1000=11008×125+(0.8+8)×125(1)(0.8+8)×125=0.8×125+8=100+8=108×乘法分配律解答(2)(0.4×4)×2.5=0.4×2.5×4×2.5=1×10=10（0.4×4）×2.5=0.4×(4×2.5)=0.4×10=4(乘法結(jié)合律）連乘×解答2.8×1.8-0.8×2.8(1.8-0.8)=2.8×=2.8(乘法分配律）(3)2.8×1.8-0.8×2.8=2.8×(1.8-0.8)×2.8=2.8×1×2.