expand (x-y)6

expand (x-y)^6

expand (2x + 4)^4

expand (2x + 4)^4

Combinations a counting principle?

Are combinations are just an application of the counting principle?

solving a recurrence

Solve the recurrence relation: a(n) = 3a(n-1) - 3 a(n-2) + a(n-3), a0=1, a1=1, a2=2 -where the value in brackets reads sub. a(n) is 'a' subscript 'n'

finding a recurrence

find and solve a recurrence relation for the number of ways to make a pile of n chips using red, white, and blue chips and such that no two red chips are together.