Explain the following derivation

Question

Can you explain the derivation in the given image? Which steps lead to the incorrect conclusion?

Answer 1

The error lies in the fact that $a^2=b^2$ does not imply $a=b$.

The third line from the last reads $(-0.5)^2 = 0.5^2$.

Then, they erroneously derived $-0.5=0.5$ and promptly added $6.5$ to both sides, leaving you with $6=7$.