Answer: 76 ft2
Explanation:
Perimeter = 2 side length +base length
40 = 2s +12
Solving for s:
40-12 =2s
28 =2s
28/2=s
14ft =side
Since the line which bisects and isosceles triangles is at a right angle to the base we can use the Pythagorean Theorem to find the height (see attachment)
c^2 = a^2 + b^2
Where c is the hypotenuse of the triangle (in this case 14) and a and b are the other sides. (Base divided by 2 is one side, the other side is the height)
Replacing with the values given:
14^2= 6^2 + x^2
196 = 36 + x^2
196-36 = x^2
160 = x^2
√160 = x
x = 12.64 (height)
Area of an isosceles triangle = 1/2 x base x height
A = 1/2 x 12 x 12.64 = 76 ft2