I need help with an algebra problem

Algebra
Tutor: None Selected Time limit: 1 Day

Nov 30th, 2015

Thank you for the opportunity to help you with your question!

The formula is  S = a(1-r^n)/(1-r)

in the first question r = 4 , n= 4 and a = 4
so, S = (4) (1- (4)^4) /(1-4)) = 4( 1  - 256)/ -3 = 4 *255/3 = 4*85 = 340


in the second question , r = (-1/2) , n= 7 and a = (-1/2)

so, S = (-1/2) ( 1 - (-1/2)^7) / ( 1-(-1/2)) = (-1/2)( 1 + 1/128) / 3/2 = - 129/ 384

Let me know incase you need any further help ! Thanks :)
Nov 30th, 2015

I'm being told that the 1st answer is wrong

Nov 30th, 2015

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