Find the sum of the geometric sequence.

1, one divided by four, one divided by sixteen, one divided by sixty four, one divided by two hundred and fifty six

Question

Find the sum of the geometric sequence. 

1, one divided by four, one divided by sixteen, one divided by sixty four, one divided by two hundred and fifty six

anonymous · Answer

if you could help it would be appreciated @ganeshie8 @mathslover @tkhunny @mathmale

anonymous · Answer

i understand you must use the formula sum=n(a1+an)/2

anonymous · Answer

but im just having a hard time plugging in the numbers as i cannot distinguish the n value would i need to do the an=a1+(n-1)d formula

anonymous · Answer

if thats necessary i got -54

anonymous · Answer

Well all I can say it that it is being multiplied by 4, but that was probably obvious :/

anonymous · Answer

wait i posted the wrong question

anonymous · Answer

Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .