Câu 1[tex]a^2=bc\Leftrightarrow\frac{c}{a}=\frac{a}{b}=\frac{c-a}{a-b}=\frac{c+a}{a+b}\Leftrightarrow \frac{a+b}{a-b}=\frac{c+a}{c-a}[/tex] (ĐPCM)
Câu 2
Vì $bc=a^2$
[tex]\frac{a^2+c^2}{b^2+a^2}=\frac{bc+c^2}{b^2+bc}=\frac{c(b+c)}{b(b+c)}=\frac{c}{b}[/tex] (ĐPCM)