oops, how embarassing! You are right, of course, Zion! Thanks for pointing it out. My only excuse is that I got only 4 hours sleep last night, due to a somewhat loud party in the neighbourhood.
At any rate you proved my point of never taking anything for granted and always checking the facts
The trick with such equations is usually that you discreetly multiply with zero and then cancel down. In this case, however, it works differently:
Line #1 reads as -15 = -15
which is correct
Line #2 says 1 = 1
Line #3 states -1² = +1²
which is basically correct, as both is 1 but
then at line #4 you radicate again which you shouldn't, because -1 is not
So line #4 is definitely wrong, and then the last line automatically gets wrong as well.