Combination principle:

An empty set is also a subset, that is, 1 elements have no cn0.

The set contains 1 elements, and cn is 1.

This collection contains two elements: cn2.

Assemble.

Cnn has n elements.

Cn0+cn 1+。 +cnn=2 n+ 1 power.

There should be proof in the textbook.

For example, the set {0, 1} has four subsets that are empty sets, namely {1}, {2} and {1, 2}, and there are * * * exactly quadratic powers of 2 in total.

The subsets of the sample set {0, 1, 2} are empty sets {0}, {1}, {2}, {0, 1}, {0,2}, {1, 2}, {0,0.

From this, we can draw our guess from the special case and finally prove it.

This is a good mathematical method.