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