`12)` `4\sqrt{24}-2\sqrt{54}+3\sqrt{6}-\sqrt{150}`

`=4.2\sqrt{6}-2.3\sqrt{6}+3\sqrt{6}-5\sqrt{6}`

`=8\sqrt{6}-6\sqrt{6}-5\sqrt{6}`

`=0`

`13)` `\sqrt{0,4}+\sqrt{2,5}`

`=(\sqrt{10})/5+(\sqrt{10})/2`

`=(7\sqrt{10})/(10)`

`14)` `3\sqrt{8}-4\sqrt{18}+2\sqrt{50}`

`=6\sqrt{2}-12\sqrt{2}+10\sqrt{2}`

`=4\sqrt{2}`

`15)` `\sqrt{75}+\sqrt{48}-\sqrt{300}`

`=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}`

`=-\sqrt{3}`

`16)` `\sqrt{20}-2\sqrt{45}+3\sqrt{80}-\sqrt{320}`

`=2\sqrt{5}-6\sqrt{5}+12\sqrt{5}-8\sqrt{5}`

`=0`

`17)` `2\sqrt{5}-\sqrt{125}-\sqrt{80}`

`=2\sqrt{5}-5\sqrt{5}-4\sqrt{5}`

`=-7\sqrt{5}`

`18)` `\sqrt{2}+5\sqrt{8}-2\sqrt{50}`

`=\sqrt{2}+10\sqrt{2}-10\sqrt{2}`

`=\sqrt{2}`

Đáp án+Giải thích các bước giải:

$\bullet$ 12) $4\sqrt{24}-2\sqrt{54}+3\sqrt{6}-\sqrt{150}$

$=4\sqrt{4.6}-2\sqrt{9.6}+3\sqrt{6}-\sqrt{25.6}$

$=4.2\sqrt{6}-2.3\sqrt{6}+3\sqrt{6}-5\sqrt{6}$

$=8\sqrt{6}-6\sqrt{6}+3\sqrt{6}-5\sqrt{6}$

$=0$

$\bullet$ 13) $\sqrt{0,4}+\sqrt{2,5}$

$=\sqrt{\dfrac{4}{10}}+\sqrt{\dfrac{25}{10}}$

$=\dfrac{\sqrt{4}}{\sqrt{10}}+\dfrac{\sqrt{25}}{\sqrt{10}}$

$=\dfrac{2}{\sqrt{10}}+\dfrac{5}{\sqrt{10}}$

$=\dfrac{7}{\sqrt{10}}$

$=\dfrac{7\sqrt{10}}{10}$

$\bullet$ 14) $3\sqrt{8}-4\sqrt{18}+2\sqrt{50}$

$=3\sqrt{4.2}-4\sqrt{9.2}+2\sqrt{25.2}$

$=3.2\sqrt{2}-4.3\sqrt{2}+2.5\sqrt{2}$

$=6\sqrt{2}-12\sqrt{2}+10\sqrt{2}$

$=4\sqrt{2}$

$\bullet$ 15) $\sqrt{75}+\sqrt{48}-\sqrt{300}$

$=\sqrt{25.3}+\sqrt{16.3}-\sqrt{3.100}$

$=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}$

$=-\sqrt{3}$

$\bullet$ 16) $\sqrt{20}-2\sqrt{45}+3\sqrt{80}-\sqrt{320}$

$=\sqrt{4.5}-2\sqrt{9.5}+3\sqrt{16.5}-\sqrt{64.5}$

$=2\sqrt{5}-2.3\sqrt{5}+3.4\sqrt{5}-8\sqrt{5}$

$=2\sqrt{5}-6\sqrt{5}+12\sqrt{5}-8\sqrt{5}$

$=0$

$\bullet$ 17) $2\sqrt{5}-\sqrt{125}-\sqrt{80}$

$=2\sqrt{5}-\sqrt{25.5}-\sqrt{16.5}$

$=2\sqrt{5}-5\sqrt{5}-4\sqrt{5}$

$=-7\sqrt{5}$

$\bullet$ 18) $\sqrt{2}+5\sqrt{8}-2\sqrt{50}$

$=\sqrt{2}+5\sqrt{2.4}-2\sqrt{2.25}$

$=\sqrt{2}+5.2\sqrt{2}-2.5\sqrt{2}$

$=\sqrt{2}+10\sqrt{2}-10\sqrt{2}$

$=\sqrt{2}$