Question

What is the value of i=

Answer 1

$\sum\limits_{t=1}^3\left(4\cdot\left(\dfrac{1}{2}\right)^{t-1}\right)=4\cdot\left(\dfrac{1}{2}\right)^{1-1}+4\cdot\left(\dfrac{1}{2}\right)^{2-1}+4\cdot\left(\dfrac{1}{2}\right)^{3-1}\\\\=4\cdot\left(\dfrac{1}{2}\right)^0+4\cdot\left(\dfrac{1}{2}\right)^1+4\cdot\left(\dfrac{1}{2}\right)^2=4\cdot1+4\cdot\dfrac{1}{2}+4\cdot\dfrac{1}{4}\\\\=4+2+1=7\\\\Answer:\ \boxed{D.\ 7}$