$a_1=-5;\ r=3;\ a_n=-405\\\\a_n=a_1r^{n-1}\\\\subtitute\\\\-5\cdot3^{n-1}=-405\ \ \ |divide\ both\ sides\ by\ (-5)\\\\3^{n-1}=81\\\\3^{n-1}=3^4\iff n-1=4\to n=5\\\\S_n=\dfrac{a_1(1-r^n)}{1-r}\\\\S_5=\dfrac{-5(1-3^5)}{1-3}=\dfrac{-5(1-243)}{-2}=\dfrac{5\cdot(-242)}{2}=5\cdot(-121)=-605\\\\\\Answer:\boxed{S_5=-605}$

4 0

3 years ago

3 miles = how many feet

LUCKY_DIMON [66]

15,840 feet. best of luck mate

7 0

3 years ago

Read 2 more answers

Help!!!!!!!!!!!!<br> 10 points!!!!!!!!!!

Grace [21]

240÷90= between 2 and 3

170÷60= between 2 and 3

250÷80= between 3 and 4

140÷40= between 3 and 4

170÷70= between 2 and 3

110÷30= between 3 and 4

there we go! :)

4 0

2 years ago

*PLEASE ANSWER[MULTIPLE CHOICE] FOR BRIANLIEST* (08.01 MC)

PLEASE ANSWER[MULTIPLE CHOICE] FOR BRIANLIEST (08.01 MC)