Tiga bilangan a, b, c membentuk barisan geometri, maka nilai 1/a + 1/b +1/c =

a, b, c = a, ar, ar²

[tex] \frac{1}{a} + \frac{1}{b} + \frac{1}{c} \\ \\ = \frac{1}{a} + \frac{1}{ar} + \frac{1}{ar^{2} } \\ \\ = \frac{a^{2} r^{3}+a^{2}r^{2}+a^{2}r}{a^{3}r^{3} } \\ \\ = \frac{(a^{2}r)(r^{2} +r+1) }{(a^{2}r)ar^{2} } \\ \\ = \frac{r^{2} +r+1}{ar^{2} } [/tex]