Some explain how many planes of symmetry a cuboid

Length width and hight are all diffrent is that helps

The answer that helps me understand what planes of symmetry are and why a cuboid has that many I'll pick as best answer

Thank you :)

Martin double counted a lot of the planes of symmetry. A plane parallel to the top and bottom of the front-back faces will also be parallel to the top and bottom sides of the left-right faces, e.g.

He also counted some that aren't planes of symmetry if the 3 dimensions are different. The planes through the diagonals are planes of symmetry only if that side is a square.

So the answer should be:
3 if all dimensions are different
5 if two are the same (add the planes through the diagonals of the square faces)
9 if three are the same (a cube--add in 2 planes through the diagonals of the other 2 pairs of square faces)

http://wiki.answers.com/Q/How_many_plane… confirms this.

http://www.kshsonline.com/departments/ma… has a picture of the 3 planes.

One way of doing this is to look at one face at a time. We can divide the faces into 3 groups, front-back, left-right and top-bottom. The front face is a rectangle. It is easy to find lines of symmetry for the rectangle. There are four of them - lines parallel to the edges and through the center and the two diagonals. Imagine the rectangle and the four lines of symmetry as a cross-section of the cuboid. The lines of symmetry of the rectangle are parts of planes. If we do this with each pair of faces we get 3*4 = 12 planes of symmetry.