In fact, all the above mentioned are XYZ stereoscopic surgery. The problem can be solved from both vertical and horizontal directions, but if so, it violates the requirement of "only cutting one side".

This is an abstract thinking problem, which I saw just a few days ago, so I'm sure my method is correct, as follows:

Is it easy to get a knife from above? Cut it into a cross triangle with three knives, four blocks on six sides, and add another piece in the middle of the triangle, so it is seven blocks.

Actually, eight dollars is the same. The only change is that the knife is cut obliquely, at an angle of about 45 degrees from the horizontal plane (the front of the cake). The knife is cut in the original position, with the upper right entering and the lower left exiting, and the southeast entering and the northwest exiting.

So the three knives still look like seven pieces, but in fact there will be an intersection point in the center of the cake, which is actually eight pieces (the original triangular prism in the middle becomes a tetrahedron with opposite vertices).

Think about it? If you don't understand, try a piece of cake or tofu to make sure it's all right!