Quadratics by taking square roots: strategy

Problem

Seth solved a quadratic equation. His work is shown below, with Step 3 missing.
What could Seth have written as the result from Step 3?
12(x1)2+5=2312(x1)2=18Step 1(x1)2=36Step 2Step 3x=5 or x=7Step 4\begin{aligned} \dfrac{1}{2}(x-1)^2+5&=23 \\\\ \dfrac{1}{2}(x-1)^2&=18&\text{Step }1 \\\\ (x-1)^2&=36&\text{Step }2 \\\\ &&\text{Step }3 \\\\ x=-5&\text{ or }x=7&\text{Step }4 \end{aligned}
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