The expansion of a polynomial is done using the binomial theorem, which states that for any numbers a and b, the equation (a - b)^n is equal to the sum from k=0 to n of [n choose k] * a^(n-k) * (b^k).
In this problem, a = 14 and b = 3x.
To find the first three terms of the expansion of (14 - 3x)^n we need to substitute n, a, b into the binomial theorem equation for k = 0, k = 1, and k = 2.
When k = 0, we have:
[n choose 0] * 14^n * (3x)^0 = 14^n
When k = 1, we have:
[n choose 1] * 14^(n-1) * (3x)^1 = n*14^(n-1) * 3x
When k = 2, we have:
[n choose 2] * 14^(n-2) * (3x)^2 = [n*(n-1)/2] * 14^(n-2) * 9x^2
Note that for any positive integer n, [n choose 0] equals to 1 and [n choose 1] equals to n. Be further aware that "(3x)^1" is just 3x, and "(3x)^2" is 9x^2.
We are looking for the first three terms in the expansion of (14 - 3x)^n in descending power. Therefore, the first term is 14^n, the second term is - 3n * 14^(n-1) * x and the third term is 4.5n(n-1) * 14^(n-2) * x^2.
Taking into consideration the options we have been given, it's clear none of them represent the expressions we have found. As such, it seems there may be a mistake in the given options.