3 . 5² - 27 : 3² + 5² . 4 - 18 : 3²

= 3 . 25 - 27 : 9 + 25 . 4 - 18 : 9

= 75 - 3 + 100 - 2

= 170

a) \(3.5^2-27:3^2-5^2.4-18:3^2\)

\(=3.\left(5^2-5^2\right).27:\left(3^2-3^2\right)\)

\(=15.0.27.0\)

\(=0.0=0\)

b) 

  2x-1 là bội của x+3

=> 2x-1 chia hết cho x+3

hay [2(x+3)-7] chia hết ho x+ 3

=> 7 chia hết cho x+ 3

x+3 εεƯ(7)={1,-1,7,-7}

x+3=1                     x+3=-1                        x+3=7                    x+3= -7

x    = 1-3                 x    = -1-3                    x    = 7-3                x    = -7-3

x    = -2                  x     =  -4                     x     =4                   x    = -10

Vậy x= -2, x=-4,x= 4, x= -10

c) \(205-\left[1200-\left(4^2-2.3\right)^3\right]:40\)

\(=205-\left[1200-16-6^3\right]:40\)

\(=205-\left[1200-10^3:40\right]\)

\(=205-1200-1000:40\)

\(=205-200:40\)

\(=205-5\)

\(=200\)

M=1/4(4/1*5+8/5*13+12/13*15+16/25*41)

=1/4(1-1/5+1/5-1/13+...+1/25-1/41)

=1/4*40/41=10/41

N=1/3(6/1*7+9/7*16+...+18/43*61)

=1/3(1-1/7+...+1/43-1/61)

=1/3*60/61=20/41

=>M<N

2/5= 0,4

3/4= 0,75

18/5= 3,6

mk nghĩ vậy ko chắc chắn đúng k nhé

\(\frac{2}{5}=\frac{2x2}{5x2}=\frac{4}{10}=0,4\)

\(\frac{3}{4}=\frac{3x25}{4x25}=\frac{75}{100}=0,75\)

\(\frac{18}{5}=\frac{18x2}{5x2}=\frac{36}{10}=3,6\)

Học tốt

\(\frac{2}{5}=2:5=0,4\)

\(\frac{3}{4}=3:4=0,75\)

\(\frac{18}{5}=18:5=3,6\)

c

C

C

Hỏi thật hả. 

chịu vì em hok lớp 6

2:

a: \(=\left(2x^2-xy\right)+\left(2xz-yz\right)\)

\(=x\left(2x-y\right)+z\left(x-2y\right)=\left(x-2y\right)\left(x+z\right)\)

b: \(=\left(x^2-4y^2\right)-\left(x-2y\right)\)

\(=\left(x-2y\right)\left(x+2y\right)-\left(x-2y\right)\)

\(=\left(x-2y\right)\left(x+2y-1\right)\)

c: \(=\left(y^2+10y+25\right)-9z^2\)

\(=\left(y+5\right)^2-\left(3z\right)^2\)

\(=\left(y+5+3z\right)\left(y+5-3z\right)\)

d: \(=\left(x+2y\right)^3-\left(x-2y\right)\left(x+2y\right)\)

\(=\left(x+2y\right)\left[\left(x+2y\right)^2-\left(x-2y\right)\right]\)

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

1:

a: \(x\left(3-4x\right)+5\left(3-4x\right)=\left(3-4x\right)\left(x+5\right)\)

b: \(2y\left(5y-6\right)-4\left(6-5y\right)\)

\(=2y\left(5y-6\right)+4\left(5y-6\right)\)

\(=2\left(5y-6\right)\left(y+2\right)\)

c: \(=27\left(x-2\right)^3-3x\left(x-2\right)^2\)

\(=3\left(x-2\right)^2\cdot\left[9\left(x-2\right)-x\right]\)

\(=3\left(x-2\right)^2\left(8x-18\right)=6\left(x-2\right)^2\cdot\left(4x-9\right)\)

d: \(=6y\left(x-y\right)\left(x+y\right)-8y\left(x+y\right)^2\)

\(=2y\left(x+y\right)\left[3\left(x-y\right)-4\left(x+y\right)\right]\)

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

\(=2y\left(x+y\right)\left(-x-7y\right)\)

Bài 1

a) x(3 - 4x) + 5(3 - 4x)

= (3 - 4x)(x + 5)

b) 2y(5y - 6) - 4(6- 5y)

= 2y(5y - 6) + 4(5y - 6)

= (5y - 6)(2y + 4)

= 2(5y - 6)(y + 2)

c) 27(x - 2)³ - 3x(2 - x)²

= 27(x - 2)³ - 3x(x - 2)²

= 3(x - 2)²[9(x - 2) - x]

= 3(x - 2)²(9x - 18 - x)

= 3(x - 2)²(8x - 18)

= 6(x - 2)²(4x - 9)

d) 6y(x² - y²) - 8y(x + y)²

= 6y(x - y)(x + y) - 8y(x + y)²

= 2y(x + y)[3(x - y) - 4(x + y)]

= 2y(x + y)(3x - 3y - 4x - 4y)

= 2y(x + y)(-x - 7y)

= -2y(x + y)(x + 7y)

\(a,50\%x-0,2+x=\dfrac{4}{5}\)

\(\Leftrightarrow\dfrac{1}{2}x-0,2+x=\dfrac{4}{5}\)

\(\Leftrightarrow\dfrac{1}{2}x+x=\dfrac{4}{5}+0,2\)

\(\Leftrightarrow\dfrac{3}{2}x=\dfrac{4}{5}+\dfrac{1}{5}\)

\(\Leftrightarrow\dfrac{3}{2}x=1\)

\(\Leftrightarrow x=\dfrac{2}{3}\)

\(b,\left(x-\dfrac{3}{4}\right):\dfrac{1}{2}+\dfrac{3}{2}=\dfrac{25}{2}\)

\(\Leftrightarrow\left(x-\dfrac{3}{4}\right).2=\dfrac{25}{2}-\dfrac{3}{2}\)

\(\Leftrightarrow\left(x-\dfrac{3}{4}\right).2=\dfrac{22}{2}\)

\(\Leftrightarrow x-\dfrac{3}{4}=11:2\)

\(\Leftrightarrow x=\dfrac{11}{2}+\dfrac{3}{4}\)

\(\Leftrightarrow x=\dfrac{25}{4}\)