Question 53431
I think you mean:
{{{sqrt(5-x)-3=0}}}
If so, 
1. isolate your radical 
2. square both sides Remember: {{{highlight((sqrt(x))^2=x)}}}
3. solve for x
4. check by substitution, you can do everything right and still get an extraneous solution (false solution) that is not really a solution with radicals
{{{sqrt(5-x)-3+3=0+3}}}
{{{sqrt(5-x)=3}}}
{{{(sqrt(5-x))^2=3^2}}}
{{{5-x=9}}}
{{{-5+5-x=-5+9}}}
{{{-x=4}}}
{{{-(-x)=-(4)}}}
{{{x=-4}}}
Check by substituting -4 into the original equation to see if both sides equal:
{{{sqrt(5-(-4))-3=0}}}
{{{sqrt(9)-3=0}}}
{{{3-3=0}}}
{{{0=0}}}
The solution checked so:
{{{highlight(x=-4)}}}
Happy Calculating!!!