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