Square vs Rhombus

Geometry Level 1

A rhombus and a square have the same side length, but are not congruent. Which has the smaller area?

Rhombus Square They have the same area Unable to determine

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18 solutions

An Phạm
Jan 28, 2018

There is a nice, geometrical solution to the question.

Moderator note:

The parallelogram area formula is the height multiplied by the base length. It can be justified via a dissection as shown here.

The square area formula is also the height multipied by the base length.

So in words, the proof is essentially that if the square is tilted to become a rhombus, the height must necessarily be smaller; therefore the area of the parallelogram must also be smaller.

Very nice solution!

Javier Álvarez - 3 years, 4 months ago

Very clever

Alan Fruge - 3 years, 4 months ago

Isn't a square a form of a rhombus? So the answer should be rhombus <= square... which wasn't offered, so indeterminate.

Mark Harnett - 3 years, 4 months ago

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The problem stated that the rhombus and the square were not congruent.

An Phạm - 3 years, 4 months ago

Consider a square of side length = a . If we pick opposite corners and stretch them. The resulting figure will be a rhombus with side length = a . Then shouldn't they have equal area and equal perimeter.

Sachin Mishra - 3 years, 4 months ago

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If you "stretch" the square from opposite corners, the resulting rhombus will have longer side length than the square. This is more like holding one side and pushing the square over from one of the adjacent sides.

Brian Egedy - 3 years, 1 month ago

Screw geometry solution See inequality solution Let S be the common side length Let the two diagonals be D1 and D2 Then as the diagonals bisect at 90° ({D1}²/4)+({D2}²/4) = s^2 Apply am-gm 2{d1}×{d2} < 4s² ½{D1}×{D2} < s²........(1) But ½{D1}×{D2} = area of rhombus S² = area of square From (1) we get that Area of rhombus < Area of square

Arun Palaniappan - 3 years, 4 months ago

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I am going to be a grunt worker forever...because that seems to be the only good thing I can be successful at.

Christopher Carraman - 3 years, 4 months ago

oh wow nice

abc54321 abc - 3 years, 4 months ago

I guess you need to know what congruent means...

Christophe B. - 3 years, 4 months ago

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A valid point. This is mathematics, not damn literary english! ... haha.gif

ignis none - 3 years, 4 months ago

Also, if you can’t work it out, you’re therefore unable to determine the right answer, so picking the last answer should be correct;-)

Christophe B. - 3 years, 4 months ago

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Technically correct is always correct. Right?

ignis none - 3 years, 4 months ago

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according to Futurama (Hermes' boss) that's the best kind

Komninos Maraslidis - 3 years, 2 months ago

I didn't read the question and worked out the biggest area.

Duncan Schaafsma - 3 years, 4 months ago

What convinced me of the fact that the Rhombus has smaller area is that you can draw a sequence of Rhombuses of ever smaller area, having the same length sides, until you get a Rhombus that has nearly zero area.

Kermit Rose - 3 years, 1 month ago
Ashfaq Humbazi
Jan 28, 2018

Let the side length for both the figures be a a units.

Area of rhombus = a 2 sin θ a^{2}\sin\theta

Area of square = a 2 a^{2}

One can clearly see that in case of the square, θ = 9 0 o \theta = 90^{o} , so rhombus has to have the smaller area.

My solution exactly.

Alan Fruge - 3 years, 4 months ago

i think it is rombus but 2 seconds later i think it is square

maryam abood - 3 years, 4 months ago

Ashfaq, can u elaborate on your solution please? That would be helpful

Mirco Ghadri - 3 years, 4 months ago

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sin 9 0 o = 1 \sin 90^o =1 , so the square will have the largest area. This formula comes from the triangle area formula using sine. Giving 2 the length of two sides of a triangle ( a a and b b ) and the angles formed between they ( t h e t a theta , the area of this triangle will be sin θ a b 2 \sin \theta \cdot \frac{ab}{2} .

If we cut the rhombus among its diagonal, we will have two congruent triangles. Two of the sides of this triangles will be a a (side of the rhombus) and the angle between they will be θ \theta . Then the area of the rhombus can be written as \(a^2 \sin \theta).

Note that two adjacent angles in a rhombus are supplementary angles so the have the same sine. Also, the angle can only in the range \(0 < \theta < 2\pi\), and in this range the largest value for sin θ \sin \theta is 1, when θ \theta is a right angle.

Victor Paes Plinio - 3 years, 4 months ago

Exactly, but in case of θ = 9 0 o \theta = 90^{o} they are the same. Because there is no restriction to the angle we have a possible solution for equal area and thus it cannot be determined which is smaller.

Steffen Peikert - 3 years, 4 months ago
Aaryan Maheshwari
Jan 18, 2018

The area of a square is ( S i d e ) 2 (Side)^2 and the area of rhombus is B a s e × H e i g h t Base\times\space Height .

Consider the set-ups below:

Notice that A E AE is perpendicular to B C BC so, A E 2 = A B 2 B E 2 = a 2 B E 2 . AE^2=AB^2-BE^2=a^2-BE^2. So, definitely, E F > A E . EF>AE.

The rest is left to the reader.

wouldn't you have equal areas by this picture? the height in the rhombus is the same as the height of the sides in the rectangle. multiplying equal base by height or rhombus or height of rectangle is the same area. I understand the math proof with Pythagorean theorem but I am visually / geometrically confused.

Matthew Agona - 3 years, 4 months ago

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This is only a 2D representation of a 3D Reflection. For a square solid piece with equal sides to become a rombus with thoes same dimensions. The only solution in the 3D dimension, to set any one side of the square parallel to an axis(eg, x-axis), and rotate across the line of axi's ~ Axis... Now for the object to become a rombus the viewing point of image matter. For Different viewing points you get a unique representation of the object. The viewing point/plane for this problem would ideally be initially parallel to the face of the square...some y-distancd away.., then rotate that plane aproximately 33° or 45°(Aproximate Haven't actually calculated these..) on the xy plane. And then from that viewing plane when looking at the Square object; with one of its side having a Vector of (1,0,0) If (x,y,z); start rotating on the zy Plane in the positive y direction. From the viewing point the image of the Solid Square rotating to about 45° in the positive y-direction would form into and image(2d representation) of a rhombus. And the math proves this problem has a 3D solution by having mathematical proof that the height is different. This is true because the angle of the rotating Square is crearting a circle on the ZY ( A plane perpendicular to the ZY plane ). And the square was at PI/2 radians but at radians between (0,pi/2) the y-component is smaller. Therefore the height of the rhombhs is equivalent to the y-component when on the Image. This proves that a rombus is just a 2D representstion of a flat Square viewed from its front and angled down towards the ground. And math is the way humans understand the fabric of the symmetric vast yet beautiful universes.

Shahab Hassan - 3 years, 4 months ago

The square has greater area the given answer is sure wrong.

samer shoukry kossa - 3 years, 4 months ago

A very neat solution, well done :)

Daniel Podobinski - 3 years, 4 months ago

Yes. This makes sense now.

Anna Z - 3 years, 4 months ago

I drew both the rhombus and the square on a piece of blank paper then measured them, it seemed like they had an equal area. I think I should have just figured it out because the rhombus DID look a lot smaller than the square. I would rate this problem a 1 because now that I understand it, it seems fairly easy.

Lucia Tiberio - 3 years, 4 months ago

Formulas explain this much better... even more so when simply stated as in your first sentence. Thanks for this (whole) explanation!

ignis none - 3 years, 4 months ago

if the formula for square and rhombus both could be shown as 1/2 d1 d2 (similar to 1/2*d^2 for square) and they have similar side length... ugh, quite complicated for me =)

Mikhail Kozlov - 3 years, 4 months ago
Reinhard Giraud
Jan 31, 2018

Great use of applying Pythagorean theorem in the last step! +1

Pi Han Goh - 3 years, 4 months ago

Best explanation

Ruchira Moolwaney - 3 years, 4 months ago

Nailed it.

John Romanovich - 3 years, 4 months ago

Your square is rectangle?

B Motom Debbarma - 2 years, 11 months ago
Steven Yuan
Jan 28, 2018

Consider an extreme case - a rhombus that is incredibly skinny yet still has the same side length as a square. In other words, the acute angle between two adjacent sides of the rhombus is very small. Clearly, the area of the rhombus is much smaller than the area of the square, so that is our answer.

Jide Fagbuji
Jan 29, 2018

Split the Rhombus into two triangles. The area is base * height. The new base is the length of the dividing line and is always less than the length of any side. and the new height is always always less than the length of any side therefore the product of two reduced numbers cannot sum up to side*side

  • Let's recall that─ a square is an special case of rhombus. A rhombus whose one angle (consequently, each angle) is a right angle is a square.

  • The area of a rhombus with side length s s and one angle θ \theta is s 2 sin θ s^2\sin{\theta} . How? Let me provide a hint: the area of a triangle, whose one angle is θ \theta , and a a and b b are the two adjacent sides of the angle, is 1 2 a b sin θ \frac{1}{2}ab\sin{\theta} .

  • Now, as 0 < θ < 18 0 0^\circ{} <\theta< 180^\circ{} , the maximum area of a rhombus with side length s s occurs at θ = 9 0 \theta = 90^\circ{} , that is when the rhombus is also a s q u a r e square .

  • So, if the square and the rhombus are not congruent, but have equal side length, then the rhombus has smaller area .

Mike Holden
Jan 30, 2018

Solve this by looking at an extreme case. If the rhombus is completely flattened it will have zero volume. So the rhombus has less area than the square.

Yash Ghaghada
Jan 29, 2018

consider a square made of frames put that frame on ground

now give some bearings to lower two vertices and give it a push

after some time the whole frame collapses and has zero area

Lân Nguyễn
Feb 4, 2018

Let the rhombus area is S and d1, d2 are its diagonal. We have: And: a^2 is the quare area. So the rhombus has to have the smaller area.

Ankit K
Feb 4, 2018

The area of a square or rhimbus is given by a² sinA. Where a is it's an arm and A is angle between two adjacent arms. For square A=90° and for rhombus A= lesser or greater than 90°. Since sin90°=1 and for other angles between 0° to 180° it is less than 1. That's why rhombus has smaller area.

Gilberto Ramirez
Feb 3, 2018

Extend the folding of the square to the limit and it reaches zero area. So the area diminishes the moment the square starts to fold!

Jeff Phillips
Feb 2, 2018

Intuitively, if you allow the rhombus to deform further it becomes flatter until the area must become zero. Therefore, the area of any rhombus that is not a square must be less than that of the square.

Tom Fotheringham
Jan 31, 2018

The rhombus can be made be squeezing opposite corners of the square. As it is squeezed its area decreases to zero - it never increases.

Syed Hamza Khalid
Jan 31, 2018

Let the length be 2 cm:

Then the area of the square is 4 c m 2 4\ cm^2

The area of rhombus is 4 3 2 \dfrac{4\sqrt{3}}{2} .

The area of rhombus is less than the area of the square \large \color{#20A900}\therefore \text{The area of rhombus is less than the area of the square}


I found the area of the rhombus by dividing it into 4 right-angled triangles as we know that a rhombus is made of 2 equilateral triangles

Those are isosceles triangles... We get two equilateral ∆s only when one of the angles of rhombus is 60°

Toshit Jain - 3 years, 4 months ago

Imagine "pulling" from two corners of the square in order to get a rhombus, and you continued until it folds into a straight line which has zero area. So the area has to go from l^2 to 0 and the area of the rhombus is in between

Jarin Mithila
Jan 30, 2018

A Rhombus always has four equal sides; a square always has four equal sides. A square always has four 90 degree angles. The angles of a rhombus can be any measure (each pair of opposite angles will be equal, and all four will always add up to 360). A square can also be defined as a parallelogram with equal diagonals that bisect the angles. If a figure is both a rectangle (right angles) and a rhombus (equal edge lengths), then it is a square. ... A square has a larger area than any other quadrilateral with the same perimeter.

The area of a square is (side)^2 or a^2 (Considering side length = a) and the area of rhombus is Base*Height or a^2 sinϴ. the acute angle between two adjacent sides of the rhombus is very small. Clearly, the area of the rhombus is much smaller than the area of the square, so that is our answer.

Juan Bejarano
Jan 30, 2018

Base times the height.

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