Question 176368
Remember that for right triangles we have a theorem that relates the three sides, Pythagorean's Theorem.  If the two sides are a,b and the hypotenuse is c, we have that
{{{a^2+b^2=c^2}}}
So if we know the two sides are 5 and 10, we have that
{{{5^2+10^2=c^2}}}
{{{25+100=c^2}}}
{{{125=c^2}}}
{{{c=sqrt(125)}}}
Notice that 125=25*5, so 
{{{sqrt(125)=sqrt(25*5)=sqrt(25)sqrt(5)=5sqrt(5)}}}
So {{{c=5sqrt(5)}}}