<PRE><B>Question 73378</B>
{{{ sqrt(63) - 2sqrt(28) + 5sqrt(7) }}}
This is, I believe what you were trying to show as your problem.
First .. deal with {{{ sqrt(63) = sqrt(3*3*7) = 3sqrt(7) }}}
next .. deal with {{{ 2sqrt(28) = 2sqrt(2*2*7) = 4sqrt(7) }}}
{{{ 3sqrt(7) - 4sqrt(7) + 5sqrt(7) }}}
Treat the square roots as if they were variables or lables.
3 apples - 4 apples + 5 apples = 4 apples
or 
3x - 4x + 5x = 4x
so .... 
{{{ 3sqrt(7) - 4sqrt(7) + 5sqrt(7) = 4sqrt(7) }}}</PRE>