Question 1021600
You would be better off if you considered {{{ (a+sqrt(b))^2=(a^2+b)+2a*sqrt(b) }}}.
==> {{{ (a+sqrt(b))^2=(a^2+b)+2a*sqrt(b) = 28+10sqrt(3) }}}.

This implies

2a = 10 and {{{a^2+b = 28}}}
==> a = 5 and {{{5^2+b = 25+b = 28}}} ==> b = 3

Therefore,
{{{ (5+sqrt(3))^2 = 28+10sqrt(3) }}}.
Taking square roots of both sides of the last equation, we get

{{{abs(5+sqrt(3)) = sqrt(28+10sqrt(3))}}}.

But {{{abs(5+sqrt(3)) = abs(-5-sqrt(3))}}}, so now you know the answer!