6x^2-(x-3)(3x+2)-6

=6x^2-6x^2+x-9x-6-6

=-5x-12

Ta có: \(\frac{x^2+y^2}{x^2-2xy+y^2}-\frac{2}{xy}\)

\(=\frac{x^2+y^2}{\left(x-y\right)^2}-\frac{2}{xy}\)

\(=\frac{xy\left(x^2+y^2\right)-2\left(x-y\right)^2}{xy\left(x-y\right)^2}=\frac{x^3y+xy^3-2x^2+4xy-2y^2}{xy\left(x-y\right)^2}\)

TA có: \(\left(\frac{x^2+y^2}{x^2-2xy+y^2}-\frac{2}{xy}\right):\left(\frac{1}{x}-\frac{1}{y}\right)^2\)

\(=\frac{x^3y+xy^3-2x^2+4xy-2y^2}{xy\left(x-y\right)^2}:\left(\frac{y-x}{xy}\right)^2\)

\(=\frac{x^3y+xy^3-2x^2+4xy-2y^2}{xy\left(x-y\right)^2}:\frac{\left(x-y\right)^2}{x^2y^2}\)

\(=\frac{x^3y+xy^3-2x^2+4xy-2y^2}{xy\left(x-y\right)^2}\cdot\frac{x^2y^2}{\left(x-y\right)^2}=\frac{\left(x^3y+xy^3-2x^2+4xy-2y^2\right)\cdot xy}{\left(x-y\right)^4}\)

a: \(\frac{2x}{x^2+2xy}+\frac{y}{xy-2y^2}+\frac{4}{x^2-4y^2}\)

\(=\frac{2x}{x\left(x+2y\right)}+\frac{y}{y\left(x-2y\right)}+\frac{4}{\left(x-2y\right)\left(x+2y\right)}\)

\(=\frac{2}{x+2y}+\frac{1}{x-2y}+\frac{4}{\left(x-2y\right)\left(x+2y\right)}\)

\(=\frac{2\left(x-2y\right)+x+2y+4}{\left(x-2y\right)\left(x+2y\right)}=\frac{2x-4y+x+2y+4}{\left(x-2y\right)\left(x+2y\right)}\)

\(=\frac{3x-2y+4}{\left(x-2y\right)\left(x+2y\right)}\)

b:Sửa đề: \(\frac{x^2}{x^3-4x}+\frac{6}{6-3x}+\frac{1}{x+2}\)

\(=\frac{x^2}{x\left(x^2-4\right)}-\frac{6}{3\left(x-2\right)}+\frac{1}{x+2}\)

\(=\frac{x}{\left(x-2\right)\left(x+2\right)}-\frac{2}{x-2}+\frac{1}{x+2}=\frac{x-2\left(x+2\right)+x-2}{\left(x-2\right)\left(x+2\right)}\)

\(=\frac{2x-2-2x-4}{\left(x-2\right)\left(x+2\right)}=\frac{-6}{\left(x-2\right)\left(x+2\right)}\)

c: \(\frac{x^2+2}{x^3-1}+\frac{x}{x^2+x+1}+\frac{1}{1-x}\)

\(=\frac{x^2+2}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{x}{x^2+x+1}-\frac{1}{x-1}\)

\(=\frac{x^2+2+x\left(x-1\right)-\left(x^2+x+1\right)}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\frac{x^2+2+x^2-x-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{x^2-2x+1}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\frac{\left(x-1\right)^2}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{x-1}{x^2+x+1}\)

a.  3m 40cm = 340cm                             b. 4m 5dm  > 40 dm

c. 2m 5cm  > 202cm                               d. 5dm 8cm  < 60 cm

6m 5dm = 65dm            1m 65cm = 165cm

3m 3dm = 33dm            5m 10cm = 510cm

2m 9dm = 29dm            2m 2cm = 202cm

Đề bài: Viết số thích hợp vào chỗ chấm:

6m 5dm = .....dm.            1m 65cm = .....cm.

3m 3dm = .....dm.            5m 10cm = .....cm.

2m 9dm = .....dm.            2m 2cm = .....cm.

Trả lời:

6m 5dm = 65 dm.            1m 65cm = 165 cm.

3m 3dm = 33 dm.            5m 10cm = 510 cm.

2m 9dm = 29 dm.            2m 2cm = 202 cm.

Chúc bn học tốt.

-472 + (235 - 28) - (35 - 350)

= -472 + 235 - 28 - 35 + 350

= (-472 - 28) + (235 - 35) + 350

= -500 + 200 + 350

= -500 + 550

= 50

\(\left(3-x\right)\left(x+1\right)-\left(2.x\right)\left(x+2\right)-3\)

\(=3x+3-x^2-x-2x^2-4x-3=-3x^2-2x\)