Question 1208664
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Note that
{{{sqrt(r^4) = (r^4)^(1/2)^"" = r^(4*(1/2)) = r^2}}}


So we can say,
{{{S = (a^2)/(1 - sqrt(r^4))}}}


{{{S = (a^2)/(1 - r^2)}}}


{{{S(1-r^2) = a^2}}}


{{{S-S*r^2 = a^2}}}


{{{Sr^2 = S-a^2}}}


{{{r^2 = (S-a^2)/S}}}


{{{r = ""+-sqrt((S-a^2)/S)}}}


In other words,
{{{r = sqrt((S-a^2)/S)}}} or {{{r = -sqrt((S-a^2)/S)}}}
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