Which recurrence corresponds to the characteristic equation r2+1=0r^2 + 1 = 0r2+1=0?
an+an−2=0a_n + a_{n-2} = 0an+an−2=0
an−an−2=0a_n - a_{n-2} = 0an−an−2=0
an+an−1=0a_n + a_{n-1} = 0an+an−1=0
an+an−1+an−2=0a_n + a_{n-1} + a_{n-2} = 0an+an−1+an−2=0