Quadrilateral > Parallelogram > Rhombus
A rhombus is a quadrilateral / parallelogram that has FOUR (4) EQUAL SIDES but not necessarily right angles (90°) like a square or a rectangle.
A right angle is an internal angle which is equal to 90°.
NOTE: Because a rhombus is a parallelogram like a rectangle or square, opposite sides are parallel and opposite angles are equal.
INTERESTING FACT:
Any square is a rhombus, but not all rhombuses are squares.
It is helpful to think of a RHOMBUS as a SQUARE or a RECTANGLE that has been pushed from a side so that it all sides are equal in length.
AreaRhombus = altitude x S or
AreaRhombus = (d1 x d2)/2
NOTE: The ALTITUDE is the distance at right angles to two sides of a rhombus.
If you place a RHOMBUS inside of a box (a rectangle or a square) and then move one of its slanted side to the opposite side, you will get a rectangle or a square.
If all sides of the rhombus are equal and if you place a RHOMBUS inside of a box (a square but NOT a rectangle) and then fold the right or left side that are separated by a diagonal into the opposite side, you will get a rectangle that is half of the box that it is in.
KEY: Since a rhombus is basically a square that has been slanted, it can still be treated somewhat as a square. So, instead of having to learn another formula (AreaRhombus = altitude × S), simply use the rectangle formula instead.
A rhombus with a altitude of 3 in and a side of 4 in has an area of:
AreaRhombus = 3 in x 4 in = 12 in2
A rhombus with both diagonals of 4 has an area of:
AreaRhombus = 4 in x 4 in = 16 in2/2 = 8 in2
REFERENCE: See screenshots above for graphic representations.