\(\frac{a}{c}=\frac{c}{b}\Leftrightarrow a.b=c^2\)

\(\frac{a^2+a.b}{b^2+a.b}=\frac{a\left(a+b\right)}{b\left(a+b\right)}=\frac{a}{b}\)

\(\frac{\left(b+a\right)\left(b-a\right)}{a^2+a.b}=\frac{\left(b+a\right)\left(b-a\right)}{a\left(a+b\right)}=\frac{b-a}{a}\)

xl bn =)) mk đã có 1 gđ "ảo" oy, nhưng thiếu mama ... (mai tìm típ :)))