0<ba 0 < b \leq a

a=q0b+r0a = q_0 b + r_0

b=q1r0+r1b = q_1 r_0 + r_1

a=q0b+r0b=q1r0+r1r0=q2r1+r2r1=q3r2+r3=rN-1=qN+1rN+rN+1rN0=rN+1 \begin{aligned} a &= q_0 b + r_0 \\ b &= q_1 r_0 + r_1 \\ r_0 &= q_2 r_1 + r_2 \\ r_1 &= q_3 r_2 + r_3 \\ \vdots &= \vdots \\ r_{N-1} &= q_{N+1} r_N + r_{N+1} \\ & r_{N} \neq 0 = r_{N+1} \end{aligned}