Where is the error?

Algebra Level 3

I am performing the following steps to prove \(-1 = 1\).

\(-1 = i^{2}\)
\(-1=i \times i\)
\(-1 = \sqrt{-1} \times \sqrt{-1}\)
\(-1 =\sqrt{-1 \times -1}\)
\(-1 =\sqrt{1}\)
\( -1=1\)

In which step does the error exist?

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