\(\left\{{}\begin{matrix}a^2_2=a_1a_3\\a^2_3=a_2a_4\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{a_1}{a_2}=\dfrac{a_2}{a_3}\\\dfrac{a_2}{a_3}=\dfrac{a_3}{a_4}\end{matrix}\right.\)
\(\Rightarrow\dfrac{a_1}{a_2}=\dfrac{a_2}{a_3}=\dfrac{a_3}{a_4}\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{a_1}{a_2}=\dfrac{a_2}{a_3}=\dfrac{a_3}{a_4}=\dfrac{a_1a_2a_3}{a_2a_3a_4}=\dfrac{a_1}{a_4}\)
Ta có:
\(\left\{{}\begin{matrix}\dfrac{a_1}{a_2}=\dfrac{a_1^3}{a_2^3}\\\dfrac{a_2}{a_3}=\dfrac{a_2^3}{a_3^3}\\\dfrac{a_3}{a_4}=\dfrac{a_3^3}{a_4^3}\end{matrix}\right.\)
\(\Leftrightarrow\dfrac{a_1^3}{a_2^3}=\dfrac{a_2^3}{a_3^3}=\dfrac{a^3_3}{a_4^3}=\dfrac{a^3_1+a_2^3+a_3^3}{a^3_2+a^3_3+a^3_4}\)
Vậy \(\dfrac{a^3_1+a^3_2+a^3_3}{a^3_2+a^3_3+a^3_4}=\dfrac{a_1}{a_4}\)
