My friend recently proved 0=1 and i know something is wrong but i dont know what

√a × √b = √ab
only if at atleast one among a,b is positive
here both a,b is non negative so not possible
Step-by-step explanation:
Remember when expanding radicals,
[tex] \sqrt{ab} = \sqrt{a} \times \sqrt{b} [/tex]
When expanding radicals into two radicals, we don't let our radicand have two negative answers.
[tex]i = \sqrt{ - 1} [/tex]
[tex] {i}^{2} = - 1[/tex]
We don't do this
[tex] (\sqrt{ - 1} ) {}^{2} = \sqrt{ - 1 \times - 1} [/tex]
[tex] - 1 = \sqrt{1} [/tex]
[tex] - 1 = 1[/tex]