Notice: The literal factors are all the combinations of a and b where the sum of the exponents is 4: a4, a³b, a²b², ab³, b4 ... The solution to the problem of the binomial coefficients without actually ... The upper index n is the exponent of the expansion; the lower index k indicates which term ... 1a5 + a4b + a3b² + a²b3 + ab4 + b5.
