Trả lời

Bài 1:

a)(45-25).(-11)+29.(-3-17)

=20.(-11)+29.(-20)

=20.(-11)+(-29).20

=20.[(-11)+(-29)]

=20.(-30)

=-600

b)(36-6).(-5)+21.(-17-3)

=30.(-5)+21.(-20)

=(-150)+(-420)

=-570

trả lời:

a,(45-25).(-11)+29.(-3-17)

  =20.(-11)+29.(-20)

  =20.(-11)+(-29).20

  =20.[(-11)+(-29).20

  =20.(-30)

  =-600

học tốt

I

a, 117 - \(x\) = 28 - (-7)

   117 - \(x\) = 28 + 7

    117 - \(x\) = 35

            \(x\) =  117 - 35

             \(x\) = 82

b, \(x\) - (-38 - 2\(x\)) = (-3) - 8 + 2\(x\) 

    \(x\) + 38 + 2\(x\) = - 11 + 2\(x\)

   3\(x\)  + 38       = - 11 + 2\(x\)

   3\(x\) - 2\(x\)        = - 11 - 38

   \(x\)                = - 49

a) \(2x-45=\left(-4x\right)+15\)

\(2x+4x=15+45\)

\(6x=60\)

\(x=10\)

vay \(x=10\)

b) \(34-x=9+7x\)

\(-x-7x=9-34\)

\(-8x=-25\)

\(x=\frac{25}{8}\)

vay \(x=\frac{25}{8}\)

 a ) 2x + 4x = 15 + 45

    6x = 60 

     x = 10

b ) - x - 7x = 34 + 9 

     -8x = 43

      x =\(\frac{43}{-8}\)

a) \(2x-45=\left(-4x\right)+15\)

\(\Rightarrow2x+4x=45+15\)

\(\Rightarrow6x=60\)

\(\Rightarrow x=10\)

b)\(34-x=9+7x\)

\(\Rightarrow-x-7x=9-34\)

\(\Rightarrow-8x=-25\)

\(\Rightarrow x=\frac{25}{8}=3,125\)

a) \(7x\left(2x-3\right)-\left(4x^2-9\right)=0\Rightarrow7x\left(2x-3\right)-\left(2x-3\right)\left(2x+3\right)=0\Rightarrow\left(2x-3\right)\left(7x-2x+3\right)=0\Rightarrow\left[{}\begin{matrix}2x-3=0\\5x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{3}{5}\end{matrix}\right.\)

b) \(\left(2x-7\right).\left(x-2\right)\left(x^2-4\right)=0\Rightarrow\left(2x-7\right)\left(x-2\right)^2\left(x+2\right)=0\Rightarrow\left[{}\begin{matrix}2x-7=0\\\left(x-2\right)^2=0\\x+2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{7}{2}\\x=2\\x=-2\end{matrix}\right.\)

c)\(\left(9x^2-25\right)-\left(6x-10\right)=0\Rightarrow\left(3x-5\right)\left(3x+5\right)-2\left(3x-5\right)=0\Rightarrow\left(3x-5\right)\left(3x+5-2\right)=0\Rightarrow\left[{}\begin{matrix}3x-5=0\\3x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{5}{3}\\x=1\end{matrix}\right.\)

a: Ta có: \(7x\left(2x-3\right)-\left(4x^2-9\right)=0\)

\(\Leftrightarrow7x\left(2x-3\right)-\left(2x-3\right)\left(2x+3\right)=0\)

\(\Leftrightarrow\left(2x-3\right)\left(5x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=\dfrac{3}{5}\end{matrix}\right.\)

b: Ta có: \(\left(2x-7\right)\left(x-2\right)\left(x^2-4\right)=0\)

\(\Leftrightarrow\left(2x-7\right)\left(x-2\right)^2\cdot\left(x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{7}{2}\\x=2\\x=-2\end{matrix}\right.\)

c: Ta có: \(\left(9x^2-25\right)-\left(6x-10\right)=0\)

\(\Leftrightarrow\left(3x-5\right)\left(3x+5-2\right)=0\)

\(\Leftrightarrow\left(3x-5\right)\left(3x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{3}\\x=-1\end{matrix}\right.\)

a.

$7x-2y=5x-3y$

$\Leftrightarrow 2x=-y$. Thay vào điều kiện số 2 ta có:

$-y+3y=20$

$2y=20$

$\Rightarrow y=10$. 

$x=\frac{-y}{2}=\frac{-10}{2}=-5$

b.

$2x=3y\Rightarrow \frac{x}{3}=\frac{y}{2}$

$3y=4z-2y\Rightarrow 5y=4z\Rightarrow \frac{y}{4}=\frac{z}{5}$

$\Rightarrow \frac{x}{6}=\frac{y}{4}=\frac{z}{5}$

Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{6}=\frac{y}{4}=\frac{z}{5}=\frac{x+y+z}{6+4+5}=\frac{45}{15}=3$

$\Rightarrow x=6.3=18; y=4.3=12; z=5.3=15$ 

c.

$3x=4y-2x$

$\Rightarrow 5x=4y\Rightarrow x=\frac{4}{5}y$

$3x=7z-4y$

$\Leftrightarrow \frac{12}{5}y=7z-4y$

$\Leftrightarrow \frac{32}{5}y=7z\Rightarrow z=\frac{32}{35}y$

Khi đó:

$x+y-2z=10$

$\frac{4}{5}y+y-2.\frac{32}{35}y=10$

$y.\frac{-1}{35}=10$

$y=-350$

$x=\frac{4}{5}y=\frac{4}{5}.(-350)=-280$

$z=\frac{32}{35}y=\frac{32}{35}.(-350)=-320$

a)\(x^2+10x+25-y^2\)

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

\(=\left(x+5+y\right)\left(x+5-y\right)\)

b)\(5x^3-7x^2+10x-14\)

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

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

c)\(-5y^2+30y-45\)

\(=-5\left(y^2-6y+9\right)\)

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

e)\(4xy^2-8xyz+4xz^2\)

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

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

f)\(x^2+7x+10\)

\(=x^2+5x+2x+10\)

\(=x\left(x+5\right)+2\left(x+5\right)\)

\(=\left(x+2\right)\left(x+5\right)\)

k)\(2x^7+6x^6+6x^5-2x^4\)

\(=2x^4\left(x^3+3x^2+3x-1\right)\)

a)\(x^2+10x+25-y^2\)

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

\(=\left(x+5-y\right)\left(x+5+y\right)\)

b)\(5x^3-7x^2+10x-14\)

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

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

c)\(-5y^2+30y-45\)

\(=-5\left(y^2-6y+9\right)\)

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

e)\(4xy^2-8xyz+4xz^2\)

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

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

f)\(x^2+7x+10\)

\(=x^2+5x+2x+10\)

\(=x\left(x+5\right)+2\left(x+5\right)\)

k)\(2x^7+6x^6+6x^5-2x^4\)

\(=2x^4\left(x^3+3x^2+3x-1\right)\)

\(=\left(x+2\right)\left(x+5\right)\)

làm lại

1)

a) 2x + 5 = 3⁴ : 3²

2x + 5 = 3²

2x + 5 = 9

2x = 9 - 5

2x = 4

x = 4 : 2

x = 2

b) (3x - 24).73 = 2.74

(3x - 24).73 = 148

3x - 24 = 148/73

3x = 148/73 + 24

3x = 1900/73

x = 1900/73 : 3

x = 1900/219

c) [3.(42 - x)] + 15 = 23.3

126 - 3x + 15 = 69

141 - 3x = 69

3x = 141 - 69

3x = 72

x = 72 : 3

x = 24

d) 126 + (132 - x) = 300

132 - x = 300 - 126

132 - x = 174

x = 132 - 174

x = -42

2)

a) 120 - (x + 55) = 60

x + 55 = 120 - 60

x + 155 = 60

x = 60 - 55

x = 5

b) (7x - 11).3 = 25.52 + 200

(7x - 11).3 = 1500

7x - 11 = 1500 : 3

7x - 11 = 500

7x = 500 + 11

7x = 511

x = 511 : 7

x = 73

c) 2x + 2x + 4 = 544

4x = 544 - 4

4x = 540

x = 540 : 4

x = 135

3) 

a) 10 + 2x = 49 : 47

10 + 2x = 49/47

2x = 49/47 - 10

2x = -421/47

x = -421/47 : 2

x = -421/94

b) 70 - 5(x - 3) = 45

5(x - 3) = 70 - 45

5(x - 3) = 25

x - 3 = 25 : 5

x - 3 = 5

x = 5 + 3

x = 8

c) 4 + 95 : x = 143 : 142 - 23

4 + 95 : x = -3123/142

95 : x = -3123/142 - 4

95 : x = -3691/142

x = 95 : (-3691/142)

x = -13490/3691

Bài 3: 

a: x=-15

b: =>2x=18

hay x=9