数学家教你如何正确地切蛋糕

看到这个标题，很多人都会想，切蛋糕谁不会啊？然而伦敦一名数学家在YouTube视频中展示了最佳的切蛋糕方式。您别说，还真有那么点道理。

他认为传统的楔形切蛋糕方式容易让蛋糕变干，而最好的方法是从中间切并行线，取出中间长条段食用，这样剩下的蛋糕就能合并起来，如果是冰淇淋蛋糕，就能保持内部密封新鲜。

Forget everything you know about cake cutting; this new method could turn the seemingly straight-forward practice on its head.

Although, using the word ‘new’ isn’t accurate, because the method is actually a 100-year-old trick unearthed by London-based author and mathematician Alex Bellos.

In his latest YouTube video, Bellos describes how taking wedges out of cakes leaves them susceptible to drying - and we should instead be cutting them in lines so the whole cake can be sealed and stored.

Known on YouTube as Numberphile, Bellos first explained the problems with modern methods of cutting cakes.

Namely, he said that if a wedge is taken out of a cake but the rest of the food is then stored in the fridge, the edges of the cake open to the air will be ‘dry and horrible’, Bellos says.

‘You’re not maximising the amount of gastronomic pleasure that you can make from this cake.’

There is instead, he explained, a better way of cutting cakes that dates back more than a century.

The method was first published in Nature on 20 December 1906 in the letters to the editor section by English mathematical scientist Francis Galton.

Titled ‘Cutting a round cake on scientific principles’, Galton’s letter explained how the ‘ordinary method of cutting out a wedge is very faulty’.

He went on to state the cake should be cut in parallel lines, starting in the centre, with the rectangular segments of the cake then taken out and eaten.

This would allow the cake to then be closed, provided it is one with icing, keep the sponge inside sealed and retaining its freshness.

'Christmas suggests cakes, and the wish on my part [is] to describe a method of cutting them that I have recently devised to my own amusement and satisfaction.

'The problem to be solved was, "given a round tea-cake of some 5 inches across, and two persons of moderate appetite to eat it, in what way should it be cut so as to leave a minimum of exposed surface to become dry?"

'The ordinary method of cutting out a wedge is very faulty in thi s respect. The results to be aimed at are so to cut the cake that the remaining portions shall fit together.

'Consequently the chords (or the arcs) of the circumferences of these portions must be equal.

'The direction of the first two vertical planes of section is unimportant; they may be parallel, as in the first figure, or they may enclose a wedge.

'The cuts shown on the figures represent those made with the intention of letting the cake last for three days, each successive operation having removed about one-thi rd of the area of the original disc.

'A common india-rubber band embraces the whole and keeps its segments together.'

It is also recommended an elastic band is used to hold the cake together and keep it sealed.

‘I don’t know if you’ve thought about it before but these triangular slices are really annoying anyway because it’s not very satisfying,’ Bellos added.

In reference to the new method he said having ‘a nice uniform slice like that is a lot better.’

But, he concluded, most people choose to share their cakes rather than eating it themselves, meaning not much or any of it is often stored.

‘I think for the mathematical loners who don’t want to share their cakes it could be useful,’ he joked.