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