$-1=1$ . Or have I? If you think one of these steps is wrong, input your answer as the step number.

I have found a proof that
Step 1:
$-1$

Step 2:
$={ i }^{ 2 }$

Step 3:
$=i\times i$

Step 4:
$=\sqrt { -1 } \times \sqrt { -1 }$

Step 5:
$=\sqrt { -1\times -1 }$

Step 6:
$=\sqrt { 1 }$

Step 7:
$=1$

$5$
$7$
$3$
$4$
$6$
$\text{None of these choices}, -1=1 \text{ is correct}$
$1$
$2$

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The calculation rule $\sqrt { a } \times \sqrt { b } =\sqrt { ab }$ is only valid for real, non-negative values of $a$ and $b$ . Therefore step 5 is invalid.

## Source: Wikipedia: Imaginary Unit