tìm x: a/(x^2-5)(x+3)+x(x+4)(1-x)=7 b/(1-7x)(4x-3)-(14x-9)(5-2x)=30 nhanh ạ

`a)` `(x^2-5)(x+3)+x(x+4)(1-x)=7`

`<=>x^3-5x-15+3x^2+(x^2+4x)(1-x)=7`

`<=>x^3+3x^2-5x-15+x^2-x^3+4x-4x^2=7`

`<=>-x-22=0`

`<=> x=-22`

 `b)` `(1-7x)(4x-3)-(14x-9)(5-2x)=30`

`<=>-28x^2+25x-3-(-28x^2-45+88x)=30`

`<=>-28x^2+25x-3+28x^2+45-88x-30=0`

`<=>-63x+12=0`

`<=> x=\frac{4}{21}`