jika 3 bilangan a,b,c membentuk barisan geometri, maka a-b/a-2b+c =

[tex]\text{a , b , c}\\\text{a , ar , ar}^2\\\\\text{maka...}\\ \frac{a-b}{a-2b+c} \\= \frac{a - ar}{a - 2ar + ar^2}\\= \frac{a(1 - r)}{a(1-2r+r^2)}\\= \frac{1 - r}{1- 2r + r^2}\\= \frac{1 - r}{(r-1)^2}\\= - \frac{r - 1}{(r - 1)^2}\\= - \frac{1}{r-1} [/tex]

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