help me solve this equation
f[k = af[k-1 + an
Sorry, I don't understand the equation. It's not entirely clear what the equation is asking for, as there is a missing variable or constant after the "an" term. But assuming that the equation is meant to be:

f[k] = a*f[k-1] + an

where "a" and "an" are constants and "f" is a sequence of values indexed by "k", we can solve for "f[k]" recursively as follows:

f[0] = an (base case)

f[1] = af[0] + an = aan + an = (a+1)*an

f[2] = af[1] + an = a(a+1)*an + an = (a^2 + a + 1)*an

f[3] = af[2] + an = a(a^2 + a + 1)*an + an = (a^3 + a^2 + a + 1)*an

and so on.

In general, we can express f[k] as a polynomial of degree k in "a", with coefficients that depend on "an". Specifically, we have:

f[k] = (a^k + a^(k-1) + ... + a + 1)*an

This is known as a geometric series.