Find the Mistake, Then Find the Correct Answer $1 \quad x^{2}-6 x=-8$

Essay

Find the mistake, then find the correct answer.
line $1 \quad x^{2}-6 x=-8$
line $2 \quad x^{2}-6 x+9=-8+9$
line $3 \quad(x-3)^{2}=1$
line $4 \quad x-3=\sqrt{1}$
line $5 \quad x-3=1$
line $6 \quad x-3+3=1+3$
line $7 \quad x=4$
line $8 \quad$ The solution set is $\{4\}$ .