Question 1025701
{{{sqrt(-1)*sqrt(-1)=-1}}}


Try starting from {{{x^2=-1}}}.  If x is positive, {{{x^2>0}}}, which is taught and learned in introductory algebra.  {{{-1}}} is not positive.
If x is negative, then {{{x^2>0}}}, which is taught and learned in introductory algebra.  {{{-1}}} is not positive.


{{{sqrt(-1)}}}  is an imaginary unit, and is not "Real".