Question 318522
You could use Heron/Hero's formula for finding the area of a triangle when you know the lengths of the three sides, a, b, and c.
{{{A = sqrt(s(s-a)(s-b)(s-c))}}} s = the semi-perimeter of the triangle.
{{{s = 21/2}}}
{{{s = 10.5}}}
{{{a = b}}}={{{c = 21/3}}} ={{{7}}} Make the appropriate substitutions:
{{{A = sqrt(10.5(10.5-7)(10.5-7)(10.5-7))}}}
{{{A = sqrt(10.5(3.5)^3)}}}
{{{A = sqrt(10.5(42.875))}}}
{{{A = sqrt(450.1875)}}}
{{{A = 21.2}}}sq.in. (Rounded to one decimal place.)