Question

calcule a razao de uma p.a sabendo-se que a1=200 e a11 = -100

Answer 1

$<var>a_{11}=a_1+(11-1)\cdot R</var>$

$<var>-100=200+(10)\cdot R\rightarrow-300=10\cdot R\rightarrow R=\frac{-300}{10}=-30</var>$

 

 

Answer 2

$a_{11} = a_1 + 10r \\ - 100 = 200 + 10r \\ - 10r = 200 + 100 \\ - 10r = 300 \\ r = \frac{300}{- 10} \\ \boxed{r = - 30}$