a, \(\dfrac{20}{15}=\dfrac{4}{3}\)

b, \(\dfrac{6}{15}=\dfrac{2}{5}\)

c, \(\dfrac{42}{30}=\dfrac{7}{5}\)

d, \(\dfrac{40}{35}=\dfrac{8}{7}\)

e, \(\dfrac{42}{42}=1\)

g, \(\dfrac{54}{10}=\dfrac{27}{5}\)

h, \(\dfrac{12}{15}\)

k đúng để nhận câu trả lời
 

1: Sửa đề: 3x-5

\(=\dfrac{-x^2\left(3x-5\right)-3\left(3x-5\right)}{3x-5}=-x^2-3\)

2: \(=\dfrac{5x^4-5x^3+14x^3-14x^2+12x^2-12x+8x-8}{x-1}\)

=5x^2+14x^2+12x+8

3: \(=\dfrac{5x^3+10x^2+4x^2+8x+4x+8}{x+2}=5x^2+4x+4\)

4: \(=\dfrac{\left(x^2-1\right)\left(x^2+1\right)-2x\left(x^2-1\right)}{x^2-1}=x^2+1-2x\)

5: \(=\dfrac{x^2\left(5-3x\right)+3\left(5-3x\right)}{5-3x}=x^2+3\)

1/3.3/5:9/5

=1/5:9/5

=5/45=1/9

15/16:3/8*3/4

=15/16:3/8

=15/8

a \(\dfrac{1}{3}\cdot\left(\dfrac{3}{4}+\dfrac{5}{4}\right)=\dfrac{1}{3}\cdot\dfrac{8}{4}=\dfrac{1}{3}\cdot2=\dfrac{2}{3}\)

b 100

a) \(\dfrac{1}{3}\times\dfrac{3}{4}+\dfrac{5}{4}\times\dfrac{1}{3}=\dfrac{1}{3}\times\left(\dfrac{3}{4}+\dfrac{5}{4}\right)=\dfrac{1}{3}\times2=\dfrac{2}{3}\)

b) 100

a) 1/3x3/4+5/4x1/3=3/12+5/12=8/12=2/3

b) Tìm một số tự nhiên biết 3/5 số đó bằng 60

=>60:3/5=60x5/3=100

Gọi A = x2 + 2xy – 3x3 + 2y3 + 3x3 – y3

Trước hết ta thu gọn đa thức :

A = x2 + 2xy – 3x3 + 2y3 + 3x3 – y3

= (– 3x3+ 3x3) + x2 + 2xy + (2y3– y3)

= 0 + x2 + 2xy + y3.

= x2 + 2xy + y3.

Thay x = 5 ; y = 4 vào A ta được :

A = 52+ 2.5.4 + 43 = 25 + 40 + 64 = 129.

Vậy giá trị biểu thức x2 + 2xy – 3x3 + 2y3 + 3x3 – y3 tại x = 5 ; y = 4 bằng 129.

a, 5/9-1/6+1/3 =\(\dfrac{13}{18}\)                      b, 1/8:9/12+1/3=\(\dfrac{1}{2}\)

c, 5/4x4/3x3/4  = \(\dfrac{5}{4}\)                   d, 8/5x(3/7+1/4) =\(\dfrac{38}{35}\)

a)10/18-3/18+6/18

=13/18

b)1/8.12/9+1/3

=1/6+1/3

=1/6+2/6

=1/2

c)5.4.3/4.3.4=5/4

d)8/5.(12/28+7/28)

=8/5.19/28=38/35

a: \(\dfrac{5}{9}-\dfrac{1}{6}+\dfrac{1}{3}=\dfrac{13}{18}\)

b: \(\dfrac{1}{8}:\dfrac{9}{12}+\dfrac{1}{3}=\dfrac{1}{2}\)

c: \(\dfrac{5}{4}\cdot\dfrac{4}{3}\cdot\dfrac{3}{4}=\dfrac{5}{4}\)

d: \(\dfrac{8}{5}\left(\dfrac{3}{7}+\dfrac{1}{4}\right)=\dfrac{38}{35}\)

a) 3 x 5² + 15 x 2² - 26 : 2

= 3 x 25 + 15 x 4 - 13

= 75 + 60 - 13

= 135 - 13

= 122

b) 5³ x 2 - 100 : 4 + 2³ x 3

= 125 x 2 - 25 + 8 x 3

= 250 - 25 + 24

= 225 + 24

= 249

c) 3² : 5 + 2³ x 10 - 81 : 3

9 : 5 + 8 x 10 - 27

= 1,8 + 80 - 27

= 81,8 - 27

= 54,8

8/3

= 8/3

`@` `\text {Ans}`

`\downarrow`

`1.`

\(\left(-4xy\right)\cdot\left(2xy^2-3x^2y\right)\)

`=`\(\left(-4xy\right)\left(2xy^2\right)+\left(-4xy\right)\left(-3x^2y\right)\)

`=`\(-8\left(x\cdot x\right)\left(y\cdot y^2\right)+12\left(x\cdot x^2\right)\left(y\cdot y\right)\)

`=`\(-8x^2y^3+12x^3y^2\)

`2.`

\(\left(-5x\right)\left(3x^3+7x^2-x\right)\)

`=`\(\left(-5x\right)\left(3x^3\right)+\left(-5x\right)\left(7x^2\right)+\left(-5x\right)\left(-x\right)\)

`=`\(-15x^4-35x^3+5x^2\)

`3.`

\(\left(3x-2\right)\left(4x+5\right)-6x\left(2x-1\right)\)

`=`\(3x\left(4x+5\right)-2\left(4x+5\right)-12x^2+6x\)

`=`\(12x^2+15x-8x-10-12x^2+6x\)

`=`\(\left(12x^2-12x^2\right)+\left(15x-8x+6x\right)-10\)

`=`\(13x-10\)

`4.`

\(2x^2\left(x^2-7x+9\right)\)

`=`\(2x^2\cdot x^2+2x^2\cdot\left(-7x\right)+2x^2\cdot9\)

`=`\(2x^4-14x^3+18x^2\)

`5.`

\(\left(3x-5\right)\left(x^2-5x+7\right)\)

`=`\(3x\left(x^2-5x+7\right)-5\left(x^2-5x+7\right)\)

`=`\(3x^3-15x^2+21x-5x^2+25x-35\)

`=`\(3x^3-20x^2+46x-35\)