C6 1=6* 1=6
c52=5！ /(2! *3! )=5*4*3! /(2! *3! )=5*4/(2* 1)=20/2= 10
C33=3！ /3! = 1
c 6 1c52c 33 = 6 * 10 * 1 = 60
Permutation and combination formula and binomial theorem formula;
The two principles of addition and multiplication are the laws that run through. What has nothing to do with order is combination, but what needs order is arrangement.
Two formulas, two properties, two ideas and methods. Arrange and combine the summary, and the application questions must be transformed.
It is common sense to arrange and combine together and choose the back row first. Special elements and positions should be considered first.