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