7,5dm³ = 7 500cm³          \(\dfrac{1}{5}\)m³ = 200dm³          20 000cm³ = 20dm3
8,25m³ = 8 250dm³           \(\dfrac{3}{4}\)dm³ = 750cm³         219 000cm³ = 219dm3
4,053m³ = 4053dm³          \(\dfrac{1}{2}\)m³ = 500 000cm³  120 000cm³ = 0,12m³

7,5dm3=7500cm3

1/5m3=200dm3

20000cm3=20dm3

8,25m3=8250dm3

3/4dm3=750cm3

219000cm3=219dm3

tick cho mik nha.chúc các bạn học tốt

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Lời giải:
a. 

\(M=\frac{x}{\sqrt{x}(\sqrt{x}-1)}-\frac{2\sqrt{x}-1}{\sqrt{x}(\sqrt{x}-1)}=\frac{x-(2\sqrt{x}-1)}{\sqrt{x}(\sqrt{x}-1)}\\ =\frac{x-2\sqrt{x}+1}{\sqrt{x}(\sqrt{x}-1)}=\frac{(\sqrt{x}-1)^2}{\sqrt{x}(\sqrt{x}-1)}\\ =\frac{\sqrt{x}-1}{\sqrt{x}}\)

b.

$M=-2\Leftrightarrow \frac{\sqrt{x}-1}{\sqrt{x}}=-2$

$\Leftrightarrow \sqrt{x}-1=-2\sqrt{x}$

$\Leftrightarrow 3\sqrt{x}=1\Leftrightarrow x=\frac{1}{9}$ (tm)

Câu 20: C

Câu 21: B