The volume of any cylinder is
V = pi*r^2*h
where r is the radius and h is the height. We are keeping r = 2 the same the entire time, as the first part of the instructions indicate. In contrast, h is allowed to vary or change based on the values shown in the table.
If h = 1, then,
V = pi*r^2*h
V = pi*2^2*1
V = pi*4
V = 4pi
So you'll write "4pi", without quotes of course, in the V column next to h = 1. This first row shows a height of 1 leads to a volume of 4pi.
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Then if h = 2, we have,
V = pi*r^2*h
V = pi*2^2*2
V = pi*8
V = 8pi ... this is written in the second box
and finally if h = 3, we would say,
V = pi*r^2*h
V = pi*2^2*3
V = pi*12
V = 12pi .... and this is placed in the third box
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The values of V we got were: 4pi, 8pi, 12pi
This is for h = 1,2 and 3 respectively in that order.
The sequence 4,8,12 is linear because we are adding 4 each time. More specifically, it fits the equation y = 4x where x = 1,2,3. Think of y = 4x as y = 4x+0 and that fits the slope intercept form y = mx+b.