ANSWER
Yes
EXPLANATION
Your friend is correct.
First he divided both sides by 9: 36 divided by 9 is 4
Then he did the square root, which has two results: one positive and one negative. This gives +2 and -2.
Another way to check the result is to replace it into the equation. If the equation is true, then the result is correct:
[tex]\begin{gathered} 9(2)^2=36 \\ 9\cdot4=36 \\ 36=36\text{ }\rightarrow\text{ true} \\ \\ 9(-2)^2=36 \\ 9\cdot4=36 \\ 36=36\text{ }\rightarrow\text{ true} \end{gathered}[/tex]
