If a sequence an=an−1+an−2a_n = a_{n-1} + a_{n-2}an=an−1+an−2, which of these is the correct characteristic equation?
r2−r−1=0r^2 - r - 1 = 0r2−r−1=0
r2+r+1=0r^2 + r + 1 = 0r2+r+1=0
r2−r+1=0r^2 - r + 1 = 0r2−r+1=0
r2+r−1=0r^2 + r - 1 = 0r2+r−1=0