nilai dari U1+U4 adalah... a. 8. c. 10. e. 16 b. 9. d. 12

[tex]a + {ar}^{2} = 10 \: \: \: \: \: \: a(1 + {r}^{2}) = 10 \\ ar + {ar}^{3} = 5 \: \: \: \: \: ar(1 + {r}^{2} ) = 5 \\ \frac{10}{a} = \frac{5}{ar} \\ r = \frac{1}{2} \\ a(1 + {( \frac{1}{2} )}^{2} ) = 10 \\ a(1 + \frac{1}{4} ) = 10 \\ a( \frac{5}{4} ) = 10 \\ a = 8 \\ a + a {r}^{3} = 8 + 8. {( \frac{1}{2} )}^{3} = 9[/tex]