Question 867961
Expression is
{{{(2 - sqrt(5)) * (2 + sqrt(5))}}}
This is of the form (a + b)*(a - b). Using the identity
{{{(a - b)*(a + b) = a^2 - b^2}}}
The answer is
{{{2^2 - 5}}} = {{{4 - 5}}} = {{{highlight(-1)}}}

Hope you got it!