Thực hiện phép tính: a) $|-\frac{1}{2}|+9.(\sqrt{\frac{1}{81}}-2)$ b) $-21,3.54,6-45,4.21,3$

Đáp án: 

$a)$ $\left|-\dfrac{1}{2}\right|+9. \left(\sqrt{\dfrac{1}{81}}−2\right)$ $=-\dfrac{33}{2}$

$b)$ $−21,\:3.54,\:6−45,\:4.21,\:3$ $=-2130$

Giải thích các bước giải:

$a)$$\left|-\dfrac{1}{2}\right|+9. \left(\sqrt{\dfrac{1}{81}}−2\right)$

$=\dfrac{1}{2}+9\left(\sqrt{\dfrac{1}{81}}-2\right)$

$=\dfrac{1}{2}-9. \dfrac{17}{9}$

$=\dfrac{1}{2}-17$

$=-\dfrac{33}{2}$

$b)$

C1: $−21,\:3.54,\:6−45,\:4.21,\:3$

$=\left(-\dfrac{213}{10}. \dfrac{273}{5}\right)-\left(\dfrac{227}{5}. \dfrac{213}{10}\right)$

$=-\dfrac{58149}{50}-\dfrac{48351}{50}$

$=\dfrac{-106500}{50}$

$=-2130$

C2:  $−21,\:3. 54,\:6−45,\:4.21,\:3$

$=\left(−21,\:3.54,\:6\right)−\left(45,\:4. 21,\:3\right)$

$=-1162,98-967,02$

$=-2130$