This is a collection of some revision notes. They include topics discussed in first three sessions of Combinatorics Course at Cheenta (Faculty: Ashani Dasgupta).

combinatorics 1 (work sheet)

Study of symmetry in geometry is greatly facilitated by combinatorial methods
There are 6 symmetries of an equilateral triangle (=3! permutations of 3 things)
There are 8 symmetries of a square (8 out of 4! permutations of 4 things are used up)
All 24 symmetries (including orientations) of a tetrahedron account for 4! permutations of 4 things
Cycle notation helps in exploiting permutations
Length of a cycle equals it’s order
Bijection Principle helps to count sets which are otherwise difficult to count.
Number of non negative integer solutions of a + b + c + d = n is
We use balls and bars technique to do this
Partitions
Conjugate Partitions and Ferrar’s diagram
Catalan Numbers

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