Đáp án:
Giải thích các bước giải:
a, A = $\frac{1}{x-y}$ -$\frac{3xy}{x^3 +y^3}$ + $\frac{x-y}{x^2 +xy+y^2}$
⇔A = $\frac{1}{x-y}$ - $\frac{3xy}{(x-y).(x^2+xy+y^2)}$ +$\frac{x-y}{x^2+xy+y^2}$
⇔A = $\frac{1.(x^2+xy+y^2)}{(x-y).(x^2+xy+y^2)}$- $\frac{3xy}{(x-y).(x^2+xy+y^2)}$ +$\frac{(x-y).(x-y)}{(x-y).(x^2+xy+y^2)}$
⇔A = $\frac{x^2+xy+y^2-3xy+(x-y)^2}{(x-y).(x^2+xy+y^2)}$
⇔A= $\frac{x^2+xy+y^2-3xy+x^2-2xy+y^2}{(x-y).(x^2+xy+y^2)}$
⇔A = $\frac{2x^2-4xy+2y^2}{(x-y).(x^2+xy+y^2)}$
⇔A = $\frac{2.(x^2-2xy+y^2)}{(x-y).(x^2+xy+y^2)}$
⇔ A = $\frac{2.(x-y)^2}{(x-y).(x^2+xy+y^2)}$ = $\frac{2.(x-y)}{x^2+xy+y^2}$
Vậy ...
