Giải thích các bước giải:
$\begin{cases}b^2=ac\rightarrow \dfrac{b}{c}=\dfrac{a}{b}\\c^2=bd\rightarrow \dfrac{b}{c}=\dfrac{c}{d}\end{cases}\rightarrow \dfrac{a}{b}=\dfrac{b}{c}=\dfrac{c}{d}$
$\rightarrow \dfrac{a^3}{b^3}=\dfrac{b^3}{c^3}=\dfrac{c^3}{d^3}=\dfrac{abc}{bcd}=\dfrac{a^3+b^3+c^3}{b^3+c^3+d^3}$
$\rightarrow \dfrac{a^3+b^3+c^3}{b^3+c^3+d^3}=\dfrac{a}{d}\rightarrow đpcm$