So for example 
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Sum of an infinite geometric sequence with the common ratio r, and the first term a1 is 
we notice
-2 times -1/4=1/2,
1/2 times -1/4=-1/8
so a1=-2
r=-1/4 or -0.25
so the sum is
=
=
=
=
the sum is -8/5 or -1.6
we notice
-2 times -1/4=1/2,
1/2 times -1/4=-1/8
so a1=-2
r=-1/4 or -0.25
so the sum is
the sum is -8/5 or -1.6
Check the picture below.
notice, the gift box is just 6 rectangles stacked up to each other at the edges,
left and right, two rectangles of 32x40
top and bottom, two rectangles of 25x32
front and back, two rectangles of 25x40
so, just get the area of all 6 rectangles, add them up, and that's the "surface area" of the rectangular prism, and that's how much paper will be needed to cover it.
notice, the gift box is just 6 rectangles stacked up to each other at the edges,
left and right, two rectangles of 32x40
top and bottom, two rectangles of 25x32
front and back, two rectangles of 25x40
so, just get the area of all 6 rectangles, add them up, and that's the "surface area" of the rectangular prism, and that's how much paper will be needed to cover it.