Giải bài 4 trang 69

Đề bài

Tính:

$\begin{array}{c}a)2.\sqrt{6}.(-\sqrt{6});\\ b)\sqrt{1,44}-2.(\sqrt{0,6}{)}^2;\\ c)0,1.(\sqrt{7}{)}^2+\sqrt{1,69};\\ d\left)\right(-0,1).(\sqrt{120}{)}^2-\frac{1}{4}.(\sqrt{20}{)}^2\end{array}$

Lời giải chi tiết

$\begin{array}{c}a)2.\sqrt{6}.(-\sqrt{6})\\ =-2.\sqrt{6}.\sqrt{6}\\ =-2.(\sqrt{6}{)}^2\\ =-2.6\\ =-12\\ b)\sqrt{1,44}-2.(\sqrt{0,6}{)}^2\\ =1,2-2.0,6\\ =1,2-1,2\\ =0\\ c)0,1.(\sqrt{7}{)}^2+\sqrt{1,69}\\ =0,1.7+1,3\\ =0,7+1,3\\ =2\\ d\left)\right(-0,1).(\sqrt{120}{)}^2-\frac{1}{4}.(\sqrt{20}{)}^2\\ =(-0,1).120-\frac{1}{4}.20\\ =-12-5\\ =-(12+5)\\ =-17\end{array}$