Um terreno será vendido através de um plano de pagamento mensais em que o primeiro pagamento de R$50.... Pergunta de ideia deMARRCELIN

danielfalves $S_{n}= \dfrac{(a_1+a_{n})\cdot{n}}{2}\\\\\\\ 19500= \dfrac{(500+a_{n})\cdot{n}}{2}\\\\\\ 39000=500n+an\cdot{n}\\\\\\a_{n}=a_1+(n-1)\cdot{r}\\a_{n}=500+(n-1)\cdot50\\a_{n}=500+50n-50\\a_{n}=450+50n\\\\39000=500n+n\cdot(450+50n)\\39000=500n+450n+50n^2\\50n^2+950n-39000=0\\n^2+19n-780=0\\\\\triangle=b^2-4ac\\\triangle=(19)^2-4\cdot(1)\cdot(-780)\\\triangle=361+3120\\\triangle=3481\\\\n= \dfrac{-b \frac{+}{-} \sqrt{\triangle} }{2a}\\\\\\n= \dfrac{-19 \frac{+}{-} \sqrt{3481} }{2}$

$n= \dfrac{-19 \frac{+}{-}59 }{2}\\\\\\n'= -39\ (n\~ao\ serve\ como\ solu\c{c}\~ao)\\\\n"=20\\\\\boxed{20\ presta\c{c}\~oes}$

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