Làm cho mình câu 1 ạ

a. $\frac{y-2}{y^{2}-4y+4}$

= $\frac{y-2}{(y-2)^{2}}$ 

= $\frac{1}{y-2}$ 

b. $\frac{x^{3}+y^{3}}{x^{2}-xy+y^{2}}$ 

= $\frac{(x+y)(x^{2}-xy+y^{2})}{x^{2}-xy+y^{2}}$ 

= x+y

c. $\frac{x(y+3)-2y-6}{x^{2}-2x}$ 

= $\frac{x(y+3)-2(y+3)}{x(x-2)}$ 

= $\frac{(y+3)(x-2)}{x(x-2)}$ 

= $\frac{y+3}{x}$ 

d. $\frac{x^{2}-5x-6}{x^{2}-9x+18}$ 
= $\frac{x^{2}-6x+x-6}{x^{2}-3x-6x+18}$ 

= $\frac{x(x-6)+(x-6)}{x(x-3)-6(x-3)}$ 

= $\frac{(x-6)(x+1)}{(x-3)(x-6)}$ 

= $\frac{x+1}{x-3}$