Xiao Ming cut a small square with x cm side length from the dead corner of the rectangular paperboard with a cm long and B cm wide, and folded it into a paperboard without cover 1. Surface area of carton without cover 2. The volume of the paper box without cover (expressed by the algebraic formula containing a, B, x) the mathematics problem of Grade 7 is in urgent need and needs to be solved

Xiao Ming cut a small square with x cm side length from the dead corner of the rectangular paperboard with a cm long and B cm wide, and folded it into a paperboard without cover 1. Surface area of carton without cover 2. The volume of the paper box without cover (expressed by the algebraic formula containing a, B, x) the mathematics problem of Grade 7 is in urgent need and needs to be solved

Surface area: because the surface area is equal to the remaining area of the rectangle after cutting off the four corners, the surface area s = ab-4x ^ 2, the volume is equal to the bottom area times the height, the length of the bottom of the cuboid is a-2x, the width is b-2x, and the height of the cuboid is x, so the volume v = (a-2x) * (b-2x) * X

Xiaoming uses a square to cut off the four small squares on the corner to make 384, and then makes a paperboard without cover, which is 5cm in height and 405 in volume
What's the side length of this square cardboard

The height of the uncovered square is 5cm, and the side length of the square is 5cm
The volume is 405
So the bottom area = 405 / 5 = 81
The side length of the bottom surface is 9
Then the original square side length = 9 + 5 + 5 = 19