Giúp em với ạ :<<<<<<<<<<<<<<<<<<<<<<

Ta có:

$a_{2}$² = $a_{1}$ × $a_{3}$ ⇔ $\frac{a_{1}}{a_{2}}$ = $\frac{a_{2}}{a_{3}}$

$a_{3}$² = $a_{2}$ × $a_{4}$ ⇔ $\frac{a_{2}}{a_{3}}$ = $\frac{a_{3}}{a_{4}}$

⇒ $\frac{a_{1}}{a_{2}}$ = $\frac{a_{2}}{a_{3}}$ = $\frac{a_{3}}{a_{4}}$

⇔ $\frac{a_{1}³}{a_{2}³}$ = $\frac{a_{2}³}{a_{3}³}$ = $\frac{a_{3}³}{a_{4}³}$

= $\frac{a_{1}³+a_{2}³+a_{3}³}{a_{2}³+a_{3}³+a_{4}³}$ (1)

Ta có tiếp: $\frac{a_{1}³}{a_{2}³}$ = $\frac{a_{1}}{a_{2}}$ × $\frac{a_{1}}{a_{2}}$ × $\frac{a_{1}}{a_{2}}$

= $\frac{a_{1}}{a_{2}}$ × $\frac{a_{2}}{a_{3}}$ × $\frac{a_{3}}{a_{4}}$ = $\frac{a_{1}}{a_{4}}$ (2)

Từ (1)(2) ⇔ $\frac{a_{1}³+a_{2}³+a_{3}³}{a_{2}³+a_{3}³+a_{4}³}$ = $\frac{a_{1}}{a_{4}}$ (đpcm)

-----HỌC TỐT-----

#ctlhn

#human dream never stops