anh chị iu ơi giúp em với ạ 2 hoặc hai bài cũng đc

`#Bống `

`14. `

`a)MTC:x(x+6) `

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

`x/(x+6)=(x^2)/(x(x+6)) `

`b)MTC:(x-5)^2(x+5) `

`11/(25-x^2)=-11/((x-5)(x+5))=(-11(x-5))/((x-5)^2(x+5))=(-11x+55)/((x-5)^2(x+5)) `

`2/(x^2-10x+25)=2/((x-5)^2)=(2(x+5))/((x-5)^2(x+5))=(2x+10)/((x-5)^2(x+5)) `

`15. `

`a)MTC:4(x-5)(x+5) `

`2/(x+5)=(2.4(x-5))/(4(x-5)(x+5))=(8x-40)/(4(x-5)(x+5)) `

`-3/(4x-20)=-3/(4(x-5))=(-3(x+5))/(4(x+5)(x-5))=(-3x-15)/(4(x-5)(x+5)) `

`(-x+2)/(x^2-25)=(-x+2)/((x-5)(x+5))=(4(-x+2))/(4(x-5)(x+5))=(-4x+8)/(4(x-5)(x+5)) `

`b)MTC:3(x-2y)^2(x+2y) `

`1/(3x-6y)=1/(3(x-2y))=((x-2y)(x+2y))/3(x-2y)^2(x+2y)=(x^2-4y^2)/3(x-2y)^2(x+2y) `

`(-x)/(x^2-4y^2)=(-x)/((x-2y)(x+2y))=(-3x(x-2y))/3(x-2y)^2(x+2y)=(-3x^2+6xy)/3(x-2y)^2(x+2y) `

`(-2y^2)/(x^2-4xy+4y^2)=(-2y^2)/((x-2y)^2)=(-6y^2(x+2y))/3(x-2y)^2(x+2y)=(-6xy^2-12y^3)/3(x-2y)^2(x+2y) `

`16. `

`a)(9x^2+6x+1)/(9x^2-1)(x ` $\ne$ `+-1/3) `

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

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

`(9x^2+3x+1)/(27x^3-1)(x ` $\ne$ `1/3) `

`=(9x^2+3x+1)/((3x-1)(9x^2+3x+1)) `

`=1/(3x-1) `

`b) ` Vì `(3x+1)/(3x-1) `và `1/(3x-1) ` đã cùng chung mẫu thức nên không cần quy đồng.