乘法 智慧的加法
Multiplication is the addition of wisdom
⑸乘法聚化速算
看算式手撥珠,盤面演證邏輯,
推論乘法九九,理解乘即累加,
連加倍乘相通,順暢快速運算。
1=1×1=1 一個1 , 1有一個
1+1=1×2=2 二個1 , 1有二個
2+2+2=2×3=6 三個2 , 2有三個
2+2+2+2=2×4=8 2有四個
按圖示方法練習九九乘法,
盤算推演二位數及 乘10 補 0 法,
依此類推 乘百 補 二個 0 ,,,,,
8 連加九次得 8× 9 = 72
5 連加六次得 5× 6 = 30
7 連加十次得 7×10 = 70
16連加20次得 16×20 = 320
29連加百次得 29×100= 2900
利用"算式"加減化聚作乘法運算
24×15 = (20+4)×15
= 20×15 + 4 ×15
= 300 + 60 = 360
= 24×(10+5)
= 24×10 + 5×24
= 240 + 120 = 360
38×29 = (40-2)×29
= 40×29 - 2×29
= 1160 - 58 = 1102
= 38×(30-1)
= 38×30 - 38×1
= 1140 - 38 =1102
⑸ multiplication polymerization speed calculation
See the dial hand dial,
disk show logic,
Inferred multiplication ninety-nine, to understand the cumulative,
Even doubled multiplication, smooth and fast operation.
1 = 1 × 1 = 1 a 1, 1 has one
1 + 1 = 1 × 2 = 2 two 1, 1 there are two
2 + 2 + 2 = 2 × 3 = 6 three 2, 2 have three
2 + 2 + 2 + 2 = 2 × 4 = 8 2 There are four
According to the illustrated method of practice ninety multiplication,
Calculate the deduction of two digits and multiplied by 10 to fill 0 method,
And so on by one hundred plus two 0 ,,,,,
8 plus nine times 8 × 9 = 72
5 plus six times 5 × 6 = 30
7 plus 10 times 7 × 10 = 70
16 plus 20 times 16 × 20 = 320
29 plus 100 times were 29 × 100 = 2900
Using the "formula" plus and minus multiplication multiplication
24 × 15 = (20 + 4) x 15
= 20 × 15 + 4 × 15
= 300 + 60 = 360
= 24 × (10 + 5)
= 24 × 10 + 5 × 24
= 240 + 120 = 360
38 × 29 = (40-2) × 29
= 40 × 29 - 2 × 29
= 1160 - 58 = 1102
= 38 × (30-1)
= 38 × 30 - 38 × 1
= 1140 - 38 = 1102
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