Bài 2 tính nhanh a, 26×7-17×9+13×26-17×11 B,32×19+32

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1. Đáp án:

   $\text{a) 180.}$

   $\text{b) 640.}$

   Giải thích các bước giải:

   $\text{a) 26 × 7 – 17 × 9 + 13 × 26 – 17 × 11.}$

   $\text{= (26 × 7 + 13 × 26) – (17 × 9 + 17 × 11).}$

   $\text{= 26 × (7 + 13) – 17 × (9 + 11).}$

   $\text{= 26 × 20 – 17 × 20.}$

   $\text{= (26 – 17) × 20.}$

   $\text{= 9 × 20.}$

   $\text{= 180.}$

   $\text{b) 32 × 19 + 32.}$

   $\text{= 32 × 19 + 32 × 1.}$

   $\text{= 32 × (19 + 1).}$

   $\text{= 32 × 20.}$

   $\text{= 640.}$

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2. $\text{a) 26 × 7 – 17 × 9 + 13 × 26 – 17 × 11.}$

   $\text{= 26 × (7 + 13) – 17 × (9 + 11).}$

   $\text{= 26 × 20 – 17 × 20.}$

   $\text{= (26 – 17) × 20.}$

   $\text{= 9 × 20.}$

   $\text{= 180.}$

   $\text{b) 32 × 19 + 32.}$

   $\text{= 32 × (19 + 1).}$

   $\text{= 32 × 20.}$

   $\text{= 640.}$

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