What is the characteristic equation of the recurrence an=6an−1−9an−2a_n = 6a_{n-1} - 9a_{n-2}an=6an−1−9an−2?
r2+6r−9=0r^2 + 6r - 9 = 0r2+6r−9=0
r2−9r+6=0r^2 - 9r + 6 = 0r2−9r+6=0
r2−6=0r^2 - 6 = 0r2−6=0
r2−6r+9=0r^2 - 6r + 9 = 0r2−6r+9=0