Giải thích các bước giải:
$b^2=ac\rightarrow \dfrac{a}{b}=\dfrac{b}{c}$
$c^2=bd\rightarrow \dfrac{b}{c}=\dfrac{c}{d}$
$\rightarrow \dfrac{a}{b}=\dfrac{b}{c}=\dfrac{c}{d}=\dfrac{a+b-c}{b+c-d}$
$\rightarrow \dfrac{a^3}{b^3}=\dfrac{b^3}{c^3}=\dfrac{c^3}{d^3}=\dfrac{(a+b-c)^3}{(b+c-d)^3}=\dfrac{a^3+b^3-c^3}{b^3+c^3-d^3}$
$\rightarrow đpcm$