nhân từng vế 2 tỉ số,phá ngoặc ta được x=1/3=0,(3)

THeo t/ c dãy tỉ số..

=>7x+2-(7x-1)/5x+7-(5x+1)

=7x+2-7x+1/5x+7-5x-1=3/6=1/2

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

=>14x+4=5x+7

=>14x-5x=7-4

=>9x=3=>x=1/3

ảnh đẹp đó bạn

Chờ chút,giải lại cho

7x + 2 = 7x-1 va 5x+7=5x+1 la pt vo nghiem

Ta có : 

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

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

\(=>35x^2+7x+10x+2=35x^2+49x-5x-7\)

\(=>35x^2+17x+2=35x^2+44x-7\)

\(=>17x+2=44x-7\)

\(=>44x-17x=2+7\)

\(=>27x=9\)

\(=>x=\frac{9}{27}=\frac{1}{3}\)

A

1, \(A=5x\left(x^2-3\right)+x^2\left(7-5x\right)-7x^2\)

\(A=5x^3-15x+7x^2-5x^3-7x^2\)

\(A=\left(5x^3-5x^3\right)+\left(7x^2-7x^2\right)-15x\)

\(A=-15x\)

Thay \(x=-5\) vào A ta được:

\(-15\cdot-5=75\)

Vậy: ....

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

\(B=x^3-3x+7x^2-5x^3-7x^2\)

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

\(B=-4x^3-3x\)

Thay \(x=10,y=-1\) vào B ta được:

\(-4\cdot10^3-3\cdot10=-4\cdot1000-3\cdot10=-4000-30=-4030\)

Vậy: ....

\(x=\frac{1}{3}\)

=>(7x+2)*(5x+1)=(5x+7)(7x-1)(t/c 2 p/s bằng nhau)

7x(5x+1)+2(5x+1)=5x(7x-1)+7(7x-1)

35x²+7x+10x+2=35x²-5x+49x-7

17x+2=44x-7

17x-44x=-7-2

-27x=-9

x=-9/-27=1/3

Vậy x=1/3

\(x=\frac{1}{3}\)

g= 35x²+15x-49x-21-35x²-28x+10x-8

g=-52x-(-29)

tại x=-3 ta có 

g= -52.(-3).(-29)

g=4542

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(=35x^2+15x-49x-21-35x^2+28x-10x+8\)

\(=-16x-13\)

Thay x = -3 \(\Rightarrow G=35\)

Vậy G = 35 khi x = -3

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(=\left(35x^2+15x-49x-21\right)-\left(35x^2-28x+10x-8\right)\)

\(=35x^2+15x-49x-21-35x^2+28x-10x+8\)

\(=-16x-13\)

Thay \(=-3\) vào biểu thức \(G\) , ta được :

\(G=-16x-13=-16\left(-3\right)-13=48-13=35\)

\(G=\left(5x-7\right)\left(7x+3\right)-\left(7x+2\right)\left(5x-4\right)\)

\(G=35x^2+15x-49x-21-\left(35x^2-28x+10x-8\right)\)

\(G=35x^2-34x-21-35x^2+18x+8\)

\(G=-16x-13\)(1)

Thay \(x=-3\) vào (1) ta được:

\(-16.\left(-3\right)-13=48-13=35\)

Vậy..............

Chúc bạn hcọ tốt!!!