Quadrilaterals & Polygon Areas
Areas of quadrilaterals/polygons, trapezoids, shoelace, decomposition, hexagons
What you need to know
- Area formulas. Trapezoid: , where , are the parallel sides and is the distance between them. Parallelogram: . Rhombus or kite: , half the product of the diagonals. Example: parallel sides and with height give ; diagonals and give a rhombus of area .
- Any quadrilateral. If the diagonals and cross at angle , the area is . Example: diagonals and crossing at give .
- Shoelace Theorem. For corners listed in order around the shape, area . Example: , , , give .
- Regular hexagon. With side , it is six equilateral triangles, so its area is . Its long diagonal (through the center) is , and its short diagonal (skipping one corner) is . Example: gives area and diagonals and .
- Trapezoid with its diagonals. If the diagonals cross at , the two triangles on the parallel sides are similar, and the two triangles on the legs have equal area.
- Pick's Theorem. For a polygon whose corners are lattice points (both coordinates integers), area , where counts the lattice points inside and those on the boundary. Example: the rectangle from to has and , so its area is .
How AMC 10 tests it
- Early: the area of a figure on a grid. Count squares, use Shoelace or Pick, or subtract right triangles from a rectangle around it.
- A trapezoid given by its bases and legs. Drop perpendiculars; often a -- triangle gives the height.
- A square with points on its sides, joined to make a quadrilateral inside; find the ratio of the areas.
- Regular hexagons: the area of a triangle on three of its corners, or one hexagon inside another. The answer contains .
Standard approaches
- Cut along a diagonal or drop perpendiculars to make rectangles and right triangles.
- Find the area of a big simple region and subtract the unwanted pieces.
- For figures on a grid or given by coordinates, use Shoelace directly.
- For a trapezoid with its diagonals, get all four small areas from one, using the ratio of the bases.
Worked example
Trapezoid has , , and . The diagonals meet at , and the area of triangle is . What is the area of the trapezoid?
(A) (B) (C) (D) (E)
Solution. Write for the area of triangle .
Step 1. Since , triangles and have equal angles, so they are similar, with ratio . Areas go by the square of the ratio: .
Step 2. The similarity also gives . Triangles and share the corner , and their bases and lie on line , so they have the same height. Their areas are in the ratio of their bases: .
Step 3. The two side triangles have equal area, so as well.
Step 4. Add the four pieces:
The answer is .
Pitfalls
- Using the slanted leg of a trapezoid as its height. Example: a leg of that runs sideways gives height .
- Listing corners out of order in Shoelace. That measures a different, self-crossing shape.
- Using when the diagonals are not perpendicular.
Traps that recur
- Building the frame side from 3/7 alone (e.g. 1 + 6/7 or similar), which produces the decoy answers with 49 in the denominator. (2023 AMC 10A #24)
- Assuming R must be parallel to the 1x3 rectangle or to the unit square, which finds only one of the two configurations. (2021 AMC Fall 10B #25)
- Trying to find the trapezoid's dimensions or P's location; only the ratio is determined, and the height h cancels immediately in the differences of squares. (2022 AMC 10A #23)
- Assuming the pentagon is regular, or adding four equilateral triangles plus a 'middle region' without noticing that segments FC and GD cross. (2021 AMC 10B #20)
- 1.2022 AMC 10B #2
In rhombus , point lies on segment so that , , and . What is the area of ? (Note: The figure is not drawn to scale.)

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- 2.2021 AMC Fall 10B #2
What is the area of the shaded figure shown below?

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- 3.2017 AMC 10A #3
Tamara has three rows of two -feet by -feet flower beds in her garden. The beds are separated and also surrounded by -foot-wide walkways, as shown on the diagram. What is the total area of the walkways, in square feet?

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- 4.2012 AMC 10A #2
A square with side length is cut in half, creating two congruent rectangles. What are the dimensions of one of these rectangles?
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- 5.2012 AMC 10B #2
A circle of radius 5 is inscribed in a rectangle as shown. The ratio of the length of the rectangle to its width is 2:1. What is the area of the rectangle?

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- 6.2010 AMC 10A #2
Four identical squares and one rectangle are placed together to form one large square as shown. The length of the rectangle is how many times as large as its width?

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- 7.2009 AMC 10B #4
A rectangular yard contains two flower beds in the shape of congruent isosceles right triangles. The remainder of the yard has a trapezoidal shape, as shown. The parallel sides of the trapezoid have lengths and meters. What fraction of the yard is occupied by the flower beds?

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- 8.2019 AMC 10B #8
The figure below shows a square and four equilateral triangles, with each triangle having a side lying on a side of the square, such that each triangle has side length and the third vertices of the triangles meet at the center of the square. The region inside the square but outside the triangles is shaded. What is the area of the shaded region?

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- 9.2016 AMC 10A #10
A rug is made with three different colors as shown. The areas of the three differently colored regions form an arithmetic progression. The inner rectangle is one foot wide, and each of the two shaded regions is foot wide on all four sides. What is the length in feet of the inner rectangle?

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- 10.2009 AMC 10A #14
Four congruent rectangles are placed as shown. The area of the outer square is times that of the inner square. What is the ratio of the length of the longer side of each rectangle to the length of its shorter side?

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- 11.2008 AMC 10A #10
Each of the sides of a square with area is bisected, and a smaller square is constructed using the bisection points as vertices. The same process is carried out on to construct an even smaller square . What is the area of ?
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- 12.2006 AMC 10A #7
The rectangle is cut into two congruent hexagons, as shown, in such a way that the two hexagons can be repositioned without overlap to form a square. What is ?

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- 13.2003 AMC 10B #4
Rose fills each of the rectangular regions of her rectangular flower bed with a different type of flower. The lengths, in feet, of the rectangular regions in her flower bed are as shown in the figure. She plants one flower per square foot in each region. Asters cost each, begonias each, cannas each, dahlias each, and Easter lilies each. What is the least possible cost, in dollars, for her garden?

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- 14.2002 AMC 10A #8
Betsy designed a flag using blue triangles, small white squares, and a red center square, as shown. Let be the total area of the blue triangles, the total area of the white squares, and the area of the red square. Which of the following is correct?

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- 15.2022 AMC 10B #16
The diagram below shows a rectangle with side lengths and and a square with side length . Three vertices of the square lie on three different sides of the rectangle, as shown. What is the area of the region inside both the square and the rectangle?

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- 16.2022 AMC 10A #10
Daniel finds a rectangular index card and measures its diagonal to be centimeters. Daniel then cuts out equal squares of side cm at two opposite corners of the index card and measures the distance between the two closest vertices of these squares to be centimeters, as shown below. What is the area of the original index card?

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- 17.2016 AMC 10A #11
Find the area of the shaded region.

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- 18.2014 AMC 10A #16
In rectangle , , , and points , , and are midpoints of , , and , respectively. Point is the midpoint of . What is the area of the shaded region?

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- 19.2014 AMC 10A #13
Equilateral has side length , and squares , , lie outside the triangle. What is the area of hexagon ?

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- 20.2013 AMC 10B #15
A wire is cut into two pieces, one of length and the other of length . The piece of length is bent to form an equilateral triangle, and the piece of length is bent to form a regular hexagon. The triangle and the hexagon have equal area. What is ?
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- 21.2012 AMC 10B #14
Two equilateral triangles are contained in a square whose side length is . The bases of these triangles are the opposite sides of the square, and their intersection is a rhombus. What is the area of the rhombus?
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- 22.2012 AMC 10B #19
In rectangle , , , and is the midpoint of . Segment is extended 2 units beyond to point , and is the intersection of and . What is the area of ?
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- 23.2011 AMC 10B #20
Rhombus has side length and . Region consists of all points inside the rhombus that are closer to vertex than any of the other three vertices. What is the area of ?
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- 24.2007 AMC 10A #18
Consider the -sided polygon , as shown. Each of its sides has length , and each two consecutive sides form a right angle. Suppose that and meet at . What is the area of quadrilateral ?

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- 25.2006 AMC 10B #15
Rhombus is similar to rhombus . The area of rhombus is and . What is the area of rhombus ?

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- 26.2006 AMC 10A #17
In rectangle , points and trisect , and points and trisect . In addition, , and . What is the area of quadrilateral shown in the figure?

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- 27.2005 AMC 10A #20
An equiangular octagon has four sides of length and four sides of length , arranged so that no two consecutive sides have the same length. What is the area of the octagon?
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- 28.2002 AMC 10B #17
A regular octagon has sides of length two. Find the area of .
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- 29.2001 AMC 10 #18
The plane is tiled by congruent squares and congruent pentagons as indicated. The percent of the plane that is enclosed by the pentagons is closest to

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- 30.2001 AMC 10 #15
A street has parallel curbs feet apart. A crosswalk bounded by two parallel stripes crosses the street at an angle. The length of the curb between the stripes is feet and each stripe is feet long. Find the distance, in feet, between the stripes.
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- 31.2000 AMC 10 #18
Charlyn walks completely around the boundary of a square whose sides are each km long. From any point on her path she can see exactly km horizontally in all directions. What is the area of the region consisting of all points Charlyn can see during her walk, expressed in square kilometers and rounded to the nearest whole number?
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- 32.2022 AMC 10A #23
Isosceles trapezoid has parallel sides and with and There is a point in the plane such that and What is
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- 33.2021 AMC Fall 10B #18
Three identical square sheets of paper each with side length are stacked on top of each other. The middle sheet is rotated clockwise about its center and the top sheet is rotated clockwise about its center, resulting in the -sided polygon shown in the figure below. The area of this polygon can be expressed in the form , where , , and are positive integers, and is not divisible by the square of any prime. What is

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- 34.2021 AMC 10B #20
The figure is constructed from line segments, each of which has length . The area of pentagon can be written as , where and are positive integers. What is

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- 35.2020 AMC 10A #20
Quadrilateral satisfies and Diagonals and intersect at point and What is the area of quadrilateral
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- 36.2020 AMC 10B #21
In square , points and lie on and , respectively, so that Points and lie on and , respectively, and points and lie on so that and . See the figure below. Triangle , quadrilateral , quadrilateral , and pentagon each has area What is ?

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- 37.2018 AMC 10B #24
Let be a regular hexagon with side length . Denote by , , and the midpoints of sides , , and , respectively. What is the area of the convex hexagon whose interior is the intersection of the interiors of and ?
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- 38.2016 AMC 10B #23
In regular hexagon , points , , , and are chosen on sides , , , and respectively, so lines , , , and are parallel and equally spaced. What is the ratio of the area of hexagon to the area of hexagon ?
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- 39.2014 AMC 10B #21
Trapezoid has parallel sides of length and of length . The other two sides are of lengths and . The angles at and are acute. What is the length of the shorter diagonal of ?
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- 40.2010 AMC 10A #19
Equiangular hexagon has side lengths and . The area of is of the area of the hexagon. What is the sum of all possible values of ?
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- 41.2007 AMC 10A #19
A paint brush is swept along both diagonals of a square to produce the symmetric painted area, as shown. Half the area of the square is painted. What is the ratio of the side length of the square to the brush width?

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- 42.2005 AMC 10B #23
In trapezoid we have parallel to , as the midpoint of , and as the midpoint of . The area of is twice the area of . What is ?
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- 43.2003 AMC 10B #23
A regular octagon has an area of one square unit. What is the area of the rectangle ?

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- 44.2002 AMC 10A #25
In trapezoid with bases and , we have , , , and . The area of is

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- 45.2023 AMC 10A #24
Six regular hexagonal blocks of side length unit are arranged inside a regular hexagonal frame. Each block lies along an inside edge of the frame and is aligned with two other blocks, as shown in the figure below. The distance from any corner of the frame to the nearest vertex of a block is unit. What is the area of the region inside the frame not occupied by the blocks?

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- 46.2021 AMC Fall 10B #25
A rectangle with side lengths and a square with side length and a rectangle are inscribed inside a larger square as shown. The sum of all possible values for the area of can be written in the form , where and are relatively prime positive integers. What is

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Problems © Mathematical Association of America (MAA), American Mathematics Competitions. Reproduced for non-commercial educational use. The topic note, tags and key insights are original to this site.