Giải bài 2 trang 55

Đề bài

Cho $23,456=10488.$ Tính nhẩm:

$\begin{array}{c}a)2,3.456\\ b)2,3.45,6\\ c)\left(-2,3\right).\left(-4,56\right)\\ d)\left(-2,3\right).45600\end{array}$

Lời giải chi tiết

$\begin{array}{c}a)2,3.456=23.0,1.456\\ =\mathrm{23.456.0},1=10488.0,1=1048,8.\end{array}$

$\begin{array}{c}b)2,3.45,6=\left(23.0,1\right).\left(456.0,1\right)\\ =\left(23.456\right).\left(0,1.0,1\right)\\ =10488.0,01\\ =104,88\end{array}$

$\begin{array}{c}c)\left(-2,3\right).\left(-4,56\right)\\ =\left(-23.0,1\right).\left(-456.0,01\right)\\ =10488.0,001\\ =10,488\end{array}$

$\begin{array}{c}d)\left(-2,3\right).45600\\ =\left(-23.0,1\right).\left(456.100\right)\\ =\left(-23.456\right).\left(0,1.100\right)\\ =-10488.10\\ =-104880\end{array}$

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