Question 85455
Since we have a given length and width, we can use these dimensions as legs of a triangle


Since we have a triangle with legs of 8 , 4 and a hypotenuse of x(our unknown side), we can use Pythagoreans theorem to find the unknown side.

Pythagoreans theorem
{{{a^2+b^2=c^2}}}


{{{8^2+4^2=c^2}}}  Plug in a=8 and b=4 and lets solve for c

{{{6 4 + 1 6 =  c  ^ 2}}} Square each individual term




{{{8 0 =  c  ^ 2}}} Combine like terms



{{{s q r t ( 8 0 ) = s q r t (  c  ^ 2 )}}} Take the square root of both sides



{{{s q r t ( 8 0 ) = c}}} Simplify


So our answer is

{{{c = s q r t ( 8 0 )}}}

which reduces to 


{{{c=4*sqrt(5)}}}