Triangles are one type of polygon
No.
It can be but need not be.
180 degrees
half of base times altitude.
trianle have no faces, because it is 2D figure.
This is the formula to find the hypotenuse of a right angle trianle
180 degrees
They are both polygons.They have a different number of sides/angles.
An equilateral triangle has 3 equal interior angles each measureing 60 degrees
Trianle Tri is Latin for three, angle is of obscure derivation.
it seems to me that the only polygon of your description is a square
A type of polygon is a rhombusial polygon, trysectalnict polygon, and a equilateral polygon.