Consider the geometric sequence: 1, (a+b), (a+b)^2, .....
Which term of this geometric sequence, when expanded, contains the expression 35a^4b^3?
(a+b)^n can be expanded unsing the binomial theorem. The order
of each term (the sum of the powers of a and b in the term) in the expansion
is the same, and equal to n.
The order of the term 35 a^4 b^3 is 7. So what is n?