`a)`

Mẫu số chung: `300x^4 y^3 z^3`

`2/(15x^3 y^2) = (2.20xyz^3)/(15x^3 y^2 .20xyz^3) = (40xyz^3)/(300x^4 y^3 z^3)`

`y/(10x^4 z^3) = (y.30y^3)/(10x^4 z^3 .30y^3) = (30y^4)/(300x^4 y^3 z^3)`

`x/(20y^3 z) = (x.15x^4 z^2)/(20y^3 z.15x^4 z^2) = (15x^5 z^2)/(300x^4 y^3 z^3)`

`b)`

Mẫu số chung: `2(x^2 -9)`

`x/(2x+6) = x/(2(x+3)) = (x(x-3))/(2(x+3)(x-3)) = (x^2 -3x)/(2(x^2 -9))`

`4/(x^2 -9) = (4.2)/(2(x^2 -9)) = 8/(2(x^2 -9))`

`c)`

Mẫu số chung: `x^3 -1 = (x-1)(x^2 +x+1)`

`(2x)/(x^3 -1)` (giữ nguyên)

`(x-1)/(x^2 +x+1) = ((x-1)(x-1))/((x^2 +x+1)(x-1)) = (x^2 -2x+1)/(x^3 -1)`

`d)`

Mẫu số chung: `5(x-1)(x+1)^2`

`x/(1+2x+x^2) = x/((x+1)^2) = (x.5(x-1))/((x+1)^2 .5(x-1)) = (5x^2 -5x)/(5(x-1)(x+1)^2)`

`3/(5x^2 -5) = 3/(5(x-1)(x+1)) = (3.(x+1))/(5(x-1)(x+1)^2) = (3x+3)/(5(x-1)(x+1)^2)`.