Question 6935
The formula you need to use is the following:

{{{ sqrt( (x[1]-x[2])^2 + (y[1]-y[2])^2)) }}}

Plugging in your given values this gives:

{{{ sqrt( (-2sqrt(7)-4sqrt(7))^2 + (10-8)^2)) }}}
{{{ sqrt( 252 + 4 ) }}}
16 which is your answer.

Hope that helps.
Regards,
-Mike