a) 6x(5x + 3) + 3x(1 – 10x) = 7  

⇒ 30x²+18x+3x-30x²=7

⇒21x=7

⇒x=\(\dfrac{7}{21}\)

⇒x= \(\dfrac{1}{3}\)

b) (3x – 3)(5 – 21x) + (7x + 4)(9x – 5) = 44

⇒15x-63x²-15+63x + 63x²-35x+36x-20=44

⇒79x-35=44

⇒79x=44+35

⇒79x=79

⇒x=1

nhân chéo

\(\frac{3x+2}{5x+7}=\frac{3x-1}{5x+1}=\frac{3x+2-3x+1}{5x+7-5x-1}=\frac{3}{6}=\frac{1}{2}\)

=> 2(3x+2)=5x+7

=> 6x+4-5x-7=0

=> x-3=0

=> x=3

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

b, \(-2x+2=2\Leftrightarrow x=0\)

c, \(-2x-6=-8\Leftrightarrow x=1\)

1,3x+2/5x+7 =3x-1/5x+1

<=> 1,3x+2/5x-3x+1/5x = 1-7

<=> (1,3+2/5-3+1/5)x = -6

<=> -11/10x=-6

<=> x= -6 : (-11/10)

<=> x= 60/11

2.x+1/2x+1 = 0,5x+2/x +3

<=> 2x+1/2x-0,5x-2/1x = 3-1

<=> x(2+1/2-0,5-2 ) =2

<=>0x =2

<=> x=0 

Hinh nhu minh thay ban Kunzy Nguyen giai hoi sai

1,3x o dau ra ???????????????

1) áp dụng tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{3x+2}{5x+7}=\frac{3x-1}{5x+1}=\frac{\left(3x+2\right)-\left(3x-1\right)}{\left(5x+7\right)-\left(5x+1\right)}=\frac{3x+2-3x+1}{5x+7-5x-1}=\frac{3}{6}=\frac{1}{2}\)

suy ra :

\(\frac{3x-1}{5x+1}=\frac{1}{2}\Rightarrow\left(5x+1\right).1=\left(3x-1\right).2\)

=> 5x+1=6x-2

5x-6x=-2-1

-x=-3

x=3

2)áp dụng tính chất của dãy tỉ số bằng nhau ta có;

\(\frac{x+1}{2x+1}=\frac{0,5x+2}{x+3}=\frac{\left(x+1\right)-2.\left(0,5x+2\right)}{\left(2x+1\right)-2.\left(x+3\right)}=\frac{x+1-x-4}{2x+1-2x-6}=\frac{-3}{-5}=\frac{3}{5}\)

suy ra:

\(\frac{x+1}{2x+1}=\frac{3}{5}\Rightarrow\left(2x+1\right).3=\left(x+1\right).5\)

=>6x+3=5x+5

6x-5x=5-3

x=2

 chỉ có làm mới có ăn

=>(2x+3).(10x+2)=(5x+2).(4x+5)

=>(2x.10x)+(2x.2)+(3.10x)+(3.2)=(5x.4x)+(5x.5)+(2.4x)+(2.5)

=>20x²+4x+30x+6=20x²+25x+8x+10

=>20x²-20x²+4x-8x+30x-25x=10-6

=>0+4x-8x+30x-25x=4

=>-4x+30x-25x=4

=>26x-25x=4

=>x=4

B)=>(3x-1).(5x-34)=(40-5x).(25-3x)

=>15x²-102x-5x+34=1000-120x-125x+15x²

=>15x²-107x+34=1000-245x+15x²

=>15x²-15x²-107x+245x=1000-34

=>0-107x+245x=966

=>138x=966

=>x=7

A,=>(2x+3).(10x+2)=(5x+2).(4x+5)

=>(2x.10x)+(2x.2)+(3.10x)+(3.2)=(5x.4x)+(5x.5)+(2.4x)+(2.5)

=>20x2+4x+30x+6=20x2+25x+8x+10

=>20x2-20x2+4x-8x+30x-25x=10-6

=>0+4x-8x+30x-25x=4

=>-4x+30x-25x=4

=>26x-25x=4

=>x=4

\(\frac{3x+2}{5x+7}=\frac{3x-1}{5x+1}\)

\(\Rightarrow\left(3x+2\right)\left(5x+1\right)=\left(3x-1\right)\left(5x+7\right)\)

\(\Rightarrow15x^2+10x+3x+2=15x^2-5x+21x-7\)

\(3x=9\)

\(x=3\)

Ta có:  (3x+2)(5x+1)=(5x+7)(3x-1)   (ĐKXĐ: x khác  -7/5, x khác -1/5)

=> 15x²+13x+2=15x²+16x-7

=> 3x-9=0  =>x=3 (chọn)

Bài 2: 

a: \(\left(3x-3\right)^2-\left(5x-3\right)^2=0\)

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

\(\Leftrightarrow-2x\left(8x-6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{3}{4}\end{matrix}\right.\)

CÁC BẠN CỐ GẮNG GIÚP  MÌNH VỚI NHÉ

a: Ta có: 5x=-4y

nên \(\dfrac{x}{\dfrac{1}{5}}=\dfrac{y}{\dfrac{-1}{4}}\)

mà x+y=45

nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{x}{\dfrac{1}{5}}=\dfrac{y}{\dfrac{-1}{4}}=\dfrac{x+y}{\dfrac{1}{5}-\dfrac{1}{4}}=\dfrac{45}{-\dfrac{1}{20}}=900\)

Do đó: x=180; y=-225

b: Ta có: \(\dfrac{x}{\dfrac{1}{5}}=\dfrac{y}{\dfrac{-1}{4}}\)

nên \(\dfrac{-3x}{-\dfrac{3}{5}}=\dfrac{-2y}{\dfrac{1}{2}}\)

mà -3x-2y=24

nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{-3x}{-\dfrac{3}{5}}=\dfrac{-2y}{\dfrac{1}{2}}=\dfrac{-3x-2y}{-\dfrac{3}{5}+\dfrac{1}{2}}=\dfrac{24}{\dfrac{-1}{10}}=-240\)

Do đó: \(\left\{{}\begin{matrix}-3x=144\\-2y=-120\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-48\\y=60\end{matrix}\right.\)

thank ẹ :-Đ