Question 443369
 {{{28/(7-3sqrt(5))}}} 
Multiply by the conjugate:

{{{expr(28/(7-3sqrt(5))) * expr((7+3sqrt(5))/(7+3sqrt(5)))}}}

Simplify:

{{{(196 + 84sqrt(5))/(49 - 45)}}}
{{{(196+84sqrt(5))/4   = highlight(49 + 21sqrt(5))}}}