11
#
It has 34 triangles
A 30 sided polygon contains 28 triangles.
You see how many triangles fit into the shape and multiply by 180 degrees
11
8
#
There are 9 triangles in an 11 sided shape
A nine sided shape has 7 triangles
1o triangles
how many triangles are in a eight sided figure
A dodecagon is a 12 sided shape made from 10 triangles
answer may vary depending on how you split it
Infinitely many. Given any triangle, a line from a vertex to any point on the opposite side will give two triangles. That process can continue indefinitely.
I think there are 13 triangles in a 15 sided shape.. Because for convex shapes (Pentagons) You take 2 from how many sides there are in the same. Like 5-2= 3 triangles.. I could be wrong!
0.5*(1422-3*142) = 9869 diagonals