Question 765457
Heron's formula:


{{{
A=sqrt(s(s-a)(s-b)(s-c))
}}}
 where the semiperimeter is
{{{
s=(a+b+c)/2
}}}


a=5, b=6, c=7, s=18/2=9


by substitution and simplification we get

{{{A=6sqrt(6)}}}



:)