Confused on the Euclidean formula yet AGAIN

Question

I'm confused on what the formula is to get $s_2$ as well as $t_2$ as well as $s_3$ and $t_3$ ... I can't seem to crack it no matter how hard I try.By the way $s_0 = 1$

Answer 1

$s_i=s_{i-2}-s_{i-1}\cdot q_{i-1}$

$t_i=t_{i-2}-t_{i-1}\cdot q_{i-1}$