Question 1142672
{{{ A[f] = sqrt(3)*(a/2)^2 }}} = area of a face where {{{ a = 5 }}} cm
{{{ A[f] = ( sqrt(3)/4 )*5^2 }}}
{{{ A[t] = 4*(1/4)*sqrt(3)*25 }}} 
{{{ A[t] = 25*sqrt(3) }}} cm2 = area of tetrahedron
check the math