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Geometry reference

Area and Perimeter Formula Reference

Print nine labelled area and perimeter formula cards for common plane figures, with exact assumptions, symbol definitions and unit reminders.

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Reference · LetterReference · A4
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Use each labelled diagram with its stated assumptions. Area is measured in square units; perimeter and circumference are measured in linear units.

Download all nine fixed formula cards. This unscored reference has no separate answer key.

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Reference handout

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Reference handout
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Read the geometric condition with the formula

A height is perpendicular to its chosen base. Trapezoid bases are parallel, rhombus and kite diagonals are perpendicular, and a regular polygon apothem meets a side at a right angle.

Learning objective

What this activity builds

Choose the correct area, perimeter or circumference formula by matching its symbols and geometric conditions to a labelled plane figure.

Worked example

Which height belongs in the triangle area formula?

The height perpendicular to the chosen base.

In A = bh/2, b is the selected base. The matching height h meets that base or its supporting line at a right angle; a slanted side is not automatically the height.

Teaching notes

Make the practice count

  • Name the shape and check its stated assumptions before choosing a formula.
  • Trace each symbol on the labelled diagram before substituting a number.
  • State square units for area and linear units for perimeter or circumference.
  • Use the right-angle marker to distinguish a perpendicular height from a slanted side or diagonal.

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Math SheetGeometry referenceArea and Perimeter Formula ReferenceUse each labelled diagram with its stated assumptions. Area is measured in square units; perimeter and circumference are measured in linear units.Every diagram is illustrative and is not a measurement scale.SquaresArea: A = s^2Perimeter: P = 4sFour equal sides and four rightangles.s = side lengthArea: square units · Perimeter: linear unitsRectanglelwArea: A = lwPerimeter: P = 2(l + w)Opposite sides are equal; all fourangles are right angles.l = length; w = widthArea: square units · Perimeter: linear unitsTrianglebhacArea: A = bh/2Perimeter: P = a + b + cChoose side b as the base; h meetsits supporting line at 90 degrees.a, b, c = side lengths; h = height perpendicular to base bArea: square units · Perimeter: linear unitsParallelogrambhaArea: A = bhPerimeter: P = 2(a + b)Opposite sides are parallel andequal; h is perpendicular to base b.a, b = adjacent side lengths; h = height perpendicular to basebArea: square units · Perimeter: linear unitsRhombusd1d2hbsArea: A = d1d2/2 or A = bhPerimeter: P = 4sAll four sides are equal; thediagonals are perpendicular.d1, d2 = perpendicular diagonals; s = side length; b, h = baseand perpendicular heightArea: square units · Perimeter: linear unitsKited1d2abArea: A = d1d2/2Perimeter: P = 2(a + b)Each pair of adjacent equal sides haslength a or b; the diagonals areperpendicular.d1, d2 = perpendicular diagonals; a, b = the two distinctadjacent side lengthsArea: square units · Perimeter: linear unitsmath-sheet.comPage 1 / 2
Math SheetGeometry referenceArea and Perimeter Formula ReferenceUse each labelled diagram with its stated assumptions. Area is measured in square units; perimeter and circumference are measured in linear units.Every diagram is illustrative and is not a measurement scale.TrapezoidabhcdArea: A = (a + b)h/2Perimeter: P = a + b + c + dBases a and b are parallel; h is theirperpendicular distance.a, b = parallel base lengths; c, d = other side lengths; h =height perpendicular to both basesArea: square units · Perimeter: linear unitsCircledrcenterArea: A = pi r^2Circumference: C = 2 pi r = pi dUse pi for the ratio of circumferenceto diameter.r = radius from center to circle; d = diameter through center; d= 2rArea: square units · Circumference: linear unitsRegular Polygonasn equal sidesPerimeter: P = nsArea: A = aP/2All sides and angles are equal; n isan integer at least 3.n = number of equal sides; integer n >= 3; s = side length; a =apothem from center perpendicular to a sideArea: square units · Perimeter: linear unitsmath-sheet.comPage 2 / 2

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