Always, sometimes, never similar
Two triangles
Similar
An equilateral triangle and an equiangular trianfle
Always
Two congruent pentagons
Always
A right triangle and a scalene triangle
sometimes
An isosceles triangle and a scalene triangle
Never
A rectangle and square
Sometimes
Two isosceles trapezoids
Sometimes
Two rectangles
Sometimes
Two regular polygons
Sometimes
Two equilateral triangles
Always
A parallelogram and a trapezoid
Never
A right triangle and an acute triangle
Never
A right triange and isosceles triangle
Sometimes
Two isosceles triangles
Sometimes
Two rhombuses
Sometimes
Two right triangles
Sometimes
Two scalene triangles
Sometimes
Two regular hexagons
Always
Two regular octagons
Always
Two squares
Always