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Quadrilaterals & Polygons for CAT: Formulas, Weightage & Question Types

Regular hexagons and octagons, rhombus diagonals, trapeziums and polygon angles.

Quadrilaterals & Polygons formula sheet

Everything CAT needs from Quadrilaterals & Polygons, in one place. Bookmark it for revision; the lesson in the app explains where each line comes from and when to reach for it.

Everything for this chapter, in one place. aa is a side, hh a height, d1d_1 and d2d_2 the diagonals.

Rectangle and square

Rectangle, arealblb
Rectangle, perimeter2(l+b)2(l+b)
Rectangle, diagonall2+b2\sqrt{l^2+b^2} — the square root is not optional
Square, areaa2a^2
Square, diagonala2a\sqrt{2}
Rectangle in a circlethe diagonal is the diameter, so l2+b2=4R2l^2+b^2 = 4R^2

Parallelogram

Areabase×h=absin⁡θ\text{base} \times h = ab\sin\theta
Height versus sideh≤h \le the slant side, always — this is a hidden inequality
Diagonalsthey bisect each other
Diagonal identityd12+d22=2(a2+b2)d_1^2 + d_2^2 = 2(a^2+b^2)

Rhombus — four equal sides

Diagonalsperpendicular bisectors of each other
Area12d1d2\dfrac{1}{2}d_1d_2
Side and diagonalsd12+d22=4a2d_1^2 + d_2^2 = 4a^2
Area, from the anglea2sin⁡θa^2\sin\theta
Inradiusr=area2ar = \dfrac{\text{area}}{2a}

Trapezium

Area12(sum of the parallel sides)×h\dfrac{1}{2}(\text{sum of the parallel sides}) \times h
A leg perpendicular to both parallelsthat leg is the height
Legs extended to a pointthe two triangles are similar, in the ratio of the parallel sides

Circles in and around

A circle fits inside a quadrilateral exactly whenAB+CD=BC+ADAB + CD = BC + AD
Thenarea=r×semiperimeter\text{area} = r \times \text{semiperimeter}
A circle fits around it exactly whenopposite angles add to 180∘180^\circ

Any regular polygon, nn sides

Exterior angle360∘n\dfrac{360^\circ}{n}
Interior angle180∘(n−2)n\dfrac{180^\circ(n-2)}{n}
The quick oneinterior ++ exterior =180∘= 180^\circ
Sum of interior angles180∘(n−2)180^\circ(n-2)
Number of diagonalsn(n−3)2\dfrac{n(n-3)}{2}

Regular hexagon, side aa — six equilateral triangles

Area332a2\dfrac{3\sqrt{3}}{2}a^2
Short diagonal, spanning two sidesa3a\sqrt{3}
Long diagonal, straight across2a2a
Distance from centre to a vertexaa

Regular octagon, side aa

Area2(1+2)a22(1+\sqrt{2})a^2
Diagonal spanning two sidesa2+2a\sqrt{2+\sqrt{2}}

Limits

Each side of a quadrilateralis less than the sum of the other three
Fixed perimeterthe square has the largest area
Fixed areathe square has the smallest perimeter

The 7 Quadrilaterals & Polygons question types CAT repeats

Past CAT papers return to the same few shapes. Learn to recognise them and most questions become a known routine. Beyond these, CAT has asked 1 rarer one-off shape here.

  1. 01

    Inside a regular hexagon or octagon

  2. 02

    A rectangle under a constraint

  3. 03

    A trapezium

  4. 04

    A rhombus, which means its diagonals

  5. 05

    Areas split inside a rectangle or square

  6. 06

    Regular polygon angle arithmetic

  7. 07

    A parallelogram

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Quadrilaterals & Polygons in CAT: quick answers

How many Quadrilaterals & Polygons questions come in CAT Quant?
About 1.3 questions in a 22-question Quant section, worth roughly 4 marks. Quadrilaterals & Polygons appeared in 21 of the 24 CAT papers from 2017 to 2025, 32 questions in all, which ranks it 6 of 25 Quant chapters.
Are Quadrilaterals & Polygons questions in CAT MCQ or TITA?
25% of the Quadrilaterals & Polygons questions asked since 2017 were TITA (type in the answer, no negative marking). The rest were multiple choice.
What types of Quadrilaterals & Polygons questions does CAT ask?
CAT keeps returning to 7 question shapes in Quadrilaterals & Polygons: Inside a regular hexagon or octagon; A rectangle under a constraint; A trapezium; A rhombus, which means its diagonals; Areas split inside a rectangle or square; Regular polygon angle arithmetic; A parallelogram.

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