Question

Find A1? Given: Sn: -342, An: -512, R: -2

Answer 1

what is Sn and An

Answer 2

@Jillian_Summer

Answer 3

\[A _{n}=A _{1}R ^{n-1}\]\[S _{n}=A _{1}(R ^{n}-1)/(R-1)\]
solve and get the answer

Answer 4

I think your second equation is off @sumitprataps : \[S _{n}= A _{1}(1-R ^{n})/(1-R)\] I have the formulas and know how to plug in the information given to me; however solving it has proven challenging to both myself and professors. If you had a step by step of how to solve it I would really appreciate it! :)

Answer 5

both are valid depending on the value of R

Answer 6

That may be true but for this case you would need to stick with the original formula because if we used R-1 it would give you -3 but using 1-R gives you +3 and the signs (+/-) matter for this type of equation. @princeharryyy

Answer 7

use watever u like the answer will not change but just the theory willl.... @Jillian_Summer

Answer 8

u have to use 1-r according to the theory

Answer 9

they say whenever r is -ve u got to use 1-r

Answer 10

see (1-r^n)/(1-r) = (r^n -1)/(r-1) on taking - common

Answer 11

they both cancels out

Answer 12

from numerator n d denominator