An open rectangular cardboard box with a square base is to have a volume of 256 cm³. Find the dimensions of the box if the area of cardboard used is as small as possible.
Mark scheme
Marking points from the official mark scheme (May/June 2012). The mark or mark type is shown in brackets.
- [B1] x²h = 256
- [M1] A = x² + 4xh
- [A1] A = x² + 1024/x
- [A1√] dA/dx = 2x - 1024/x² oe
- [M1] Equate to 0 and solve
- [A1] x = 8
- [A1] h = 4
- OR
- [B1] A = (256/h) + 64√h
- [M1] dA/dh = -256/h² + 32/√h
- [A1]
- [A1√]
- [M1]
- [A1] h = 4
- [A1] x = 8
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