Find the area of an isosceles triangle with perimeter of 40 feet and a base of 12 feet. Round to the nearest whole number.

76 ft2

Step-by-step 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

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9 x 8 divided by (5-3)=36