Question

What are the first and last terms of this geometric series

Answer 1

ANSWER

E. 10 and 640


EXPLANATION


The given series is

$\sum_{i=1}^45 \times 2^{2i-1}$


To find the first term of the series we substitute i=1 to get,


$a_1 = 5 \times {2}^{2 \times 1 - 1}$


$a_1 = 5 \times {2}^{ 1} = 10$



For the last term of the series, we substitute i=4 to obtain,

$a_4 = 5 \times {2}^{2 \times 4 - 1}$


$a_4 = 5 \times {2}^{7}$



This implies that,


$a_4 = 5 \times 128 = 640$


Therefore the correct answer is E