运用
C(m,n)=C(m,m-n)
C(m+1,n)=C(m,n)+C(m,n-1)
C(2,1)+C(3,2)+……+C(10,9)
=C(2,1)+C(3,1)+……+C(10,1)
=C(2,2)+C(2,1)+C(3,1)+……+C(10,1)-1
=C(3,2)+C(3,1)+……+C(10,1)-1
……
=C(11,2)-1
=54
你写的C2^1是组合的意思吗.