Question

Does anyone know how to solve this please ??!

Answer 1

we are given

`\sum _(i=1)^3\:\left(4\cdot \left((1)/(2)\right)^(i-1)\right)`

now, we can expand it

`\sum _(i=1)^3\:\left(4\cdot \left((1)/(2)\right)^(i-1)\right)=(4*((1)/(2) )^(1-1))+(4*((1)/(2) )^(2-1))+(4*((1)/(2) )^(3-1))`

now, we can simplify it

we get

`\sum _(i=1)^3\:\left(4\cdot \left((1)/(2)\right)^(i-1)\right)=7`

option-D.......Answer