Answer:
Refraction are in parts or are reflected brokely, like light against aluminum. While a reflection, is exact. Like a mirror.
Well the shown circuit is definitely open because the lines are not connected. And it is not a parallel circuit because there would be more lines. Like a string of Christmas lights. So it must be an "open series circuit".
V1 * sin(θ) where θ is the angle v1 makes with the vertical.
To find the answer, plot down the factors for every number.
12: 1, 2 ,3 ,4, 6, 12
18: 1, 2, 3, 6, 9, 18
84: 1, 2, 3, 4, 6, 7, 12
If you noticed, the number that was common to the 3 numbers, were 1, 2, 3, and 6
And 6 is the bigger number
So 6 is your GCF
