Question 11

Evaluate 

stack sum open parentheses 2 plus 3 to the power of k close parentheses with k equals 1 below and 11 on top

Answer

stack sum space with k equals 1 below and 11 on top open parentheses 2 plus 3 to the power of k close parentheses equals sum from k equals 1 to 11 of open parentheses 2 close parentheses space plus space sum from k equals 1 to 11 of 3 to the power of k space equals space 2 open parentheses 11 close parentheses space plus space sum from k equals 1 to 11 of 3 to the power of k to the power of blank end exponent space equals 22 space plus space sum from k equals 1 to 11 of 3 to the power of k space space space space space space... open parentheses 1 close parentheses

sum from k equals 1 to 11 of 3 to the power of k space equals space 3 to the power of 1 space plus space 3 squared space plus space 3 cubed space plus space... space plus space 3 to the power of 11

T h e space t e r m s space o f space t h i s space s e q u e n c e space 3 comma space 3 squared comma space 3 cubed comma space horizontal ellipsis space f o r m s space a space G. P.

S subscript n space end subscript equals space fraction numerator a open parentheses r to the power of n space end exponent minus 1 close parentheses over denominator r minus 1 end fraction

rightwards double arrow S subscript n space equals space fraction numerator 3 open square brackets open parentheses 3 close parentheses to the power of 11 space minus 1 close square brackets over denominator 3 minus 1 end fraction

rightwards double arrow S subscript n space equals space 3 over 2 open parentheses 3 to the power of 11 space minus space 1 close parentheses
therefore space space sum from k equals 1 to 11 of 3 to the power of k space equals space 3 over 2 open parentheses 3 to the power of 11 space minus 1 close parentheses
S u b s t i t u t i n g space t h i s space v a l u e space i n space e q u a t i o n space left parenthesis 1 right parenthesis comma space w e space o b t a i n
sum from k equals 1 to 11 of open parentheses 2 space plus space 3 to the power of k close parentheses space equals 22 space plus space 3 over 2 open parentheses 3 to the power of 11 space minus 1 close parentheses

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