bài 1 tính bằng cách hợp lí nếu có thể a) 2.53.12+4.6.87-3.8.40 b)(2^8.3+2^8.7+2^8.6):2^12 d)1.5.6+2.10.12+4.20.24+9.45.54/1.3.5+2.6.10+4.12.20+9.27.4

a, 2.53.12+4.6.87-3.8.40

= 2.53.12+2.12.87-2.12.40

= 2.12.( 53+87-40)

= 24.100

= 2400

b, $( 2^{8}.3+2^{8}.7+2^{8}.6):2^{12}$

= $2^{8}.( 3+7+6):2^{12}$

= $2^{8}.16:2^{12}$

= $2^{8}.2^{4}:2^{12}$

= 1

d, $\frac{1.5.6+2.10.12+4.20.24+9.45.54}{1.3.5+2.6.10+4.12.20+9.27.45}$ 
= $\frac{2.( 1.5.3+2.10.6+4.20.12+9.45.27)}{1.3.5+2.6.10+4.12.20+9.27.45}$ 
= $\frac{2.( 1.3.5+2.6.10+4.12.20+9.27.45)}{1.3.5+2.6.10+4.12.20+9.27.45}$ 
= 2

 

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