Cuantos triangulos tienes un decagono?

In a decagon, by joining one vertex to the remaining vertices you can have 8 triangles. If you are considering all the vertices independently you will have a total of 8*10 = 80 triangles.

You can figure out this way: the sum of the interior angles of a decagon = (2n-4)*right angles or (n-2)*triangles. So a decagon will form 8 triangles.

Step-by-step explanation:

area of part 1:

a1=base*height/2=(8+2)*(8-2-2-1)/2=10*3/2=15 ft^2

area of part 2:

a2=length*width=(8+2)*1=10 ft2

area of part 3:

a3=length*width=8*2=16 ft2

total shaded area : a1+a2+a3=41 ft2

total area of the reactangle : a=16*8=128 ft2

total area of the nonshaded region : 128-41=87 ft2