Sometimes they are.
sometimes
never
Some polygons are rectangles. The vast majority are not.
Some parallelograms are squares - the ones which are equiangular (have equal angles) and are equilateral (have equal side lengths). All squares are parallelograms, but only some parallelograms are squares.
no
Sometimes they are.
Parallelograms are squares is sometimes true. Squares are parallelograms is always true. Rhomboids are parallelograms is also always true. So not all parallelograms are squares but some are.
sometimes
never
-- A parallelogram is always a quadrilateral. -- A quadrilateral is sometimes a parallelogram.
It is sometimes true that two parallelograms are similar. The could be congruent, or dissimilar in that one is not an enlargement of the other.
Some polygons are rectangles. The vast majority are not.
No, they are NEVER rectangles.
Some parallelograms are squares - the ones which are equiangular (have equal angles) and are equilateral (have equal side lengths). All squares are parallelograms, but only some parallelograms are squares.
Sometimes * * * * * Never. A parallelogram has two pairs of equal angles opposite one another. A trapezoid does not.
A rectangle - has four right-angles at the corners. A Parallelogram - has no right-angles, but has opposite angles equal. Technically - a rectangle is a parallelogram, but a parallelogram can never be a rectangle. Clarification - Actually, all rectangles are parallelograms, but not all parallelograms are rectangles. The definition of a parallelogram is that of a four-sided shape where the opposite sides are parallel. There is no angle-size limitation in the definition. Squares, rectangles and rhombuses are all parallelograms.