A triangle.
yes
Yes
Yes
All four-sided figures are quadrilaterals.
Yes because there are 540 degrees in a pentagon and 180 degrees in a triangle so 540/180 = 3 triangles.
All six-sided two dimensional figures are hexagons.
No. There are some figures that don't have a name that are five sided.
NO
no
NO, there not
A six sided figure is a hexagon.