In my notes I have the expression:

$\displaystyle a_n = 3a_{n-1} + 2a_{n-2}$

with

$\displaystyle a_0 = 1, a_1 = 2$

but I can't see how we get $\displaystyle a_0 = 1$

When I try I get

$\displaystyle 3a_{0-1} + 2a_{0-2}

= 3*-1 + 2*-2

= -3 + -4

= -7

$

so why is

$\displaystyle + 2a_{n-2}

= 4$

to get -3 + 4 = 1

obviously I am not understanding something...

can you point out where I am going wrong please?

Thanks