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Triangle area and perimeter worksheets

Identify nine right, common scalene, equilateral and isosceles triangles, then calculate area, perimeter or both from visible whole-number or decimal measurements in five selectable units.

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Identify each triangle and calculate the selected measurements. Use supplied rounded heights as given, derive an unlabelled height when needed, and round final answers to the nearest hundredth.

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Use the measurements shown on each triangle

Every sheet has nine right, common scalene, equilateral or isosceles triangles. Identify the type, then use the printed side lengths for perimeter and one-half base times perpendicular height for area.

A supplied equilateral or isosceles height is rounded and marked with ≈, so use that displayed measurement as given. When the height is hidden, derive it from the printed base and equal side lengths, then round only the final answer to the nearest hundredth.

Learning objective

What this activity builds

Classify real triangles and calculate area and perimeter from printed side lengths and supplied or derived perpendicular heights, with final answers rounded to the nearest hundredth.

Worked example

An isosceles triangle has base 8 cm, equal sides 5 cm and a displayed height of h ≈ 3 cm. What area should you report?

Area ≈ 12 cm².

Use the displayed rounded height as given: one-half × 8 × 3 = 12. The approximation symbol remains because the supplied height is a rounded measurement.

Teaching notes

Make the practice count

  • Classify the triangle before choosing which measurements can determine its height.
  • For perimeter, add the three printed side lengths, including any rounded derived sides.
  • When a rounded height is displayed, use it as given and keep the approximation symbol on the area.
  • When an equal-sided triangle omits its height, derive the height with the Pythagorean theorem and round only the final area.

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Math SheetNameScore/ 27TeacherDateTriangle area and perimeterIdentify each triangle and calculate the selected measurements. Use supplied rounded heights as given, derive an unlabelled height when needed, and round finalanswers to the nearest hundredth.1.10.8 ft12.5 ft6.3 ftType:Area:Perimeter:2.5.6 mm5.6 mm5.6 mmhh approx. 4.85 mmType:Area:Perimeter:3.4.3 in10 in10 inhh approx. 9.77 inType:Area:Perimeter:4.6.1 yd8.9 yd8.9 ydhh approx. 8.36 ydType:Area:Perimeter:5.4.9 ft8.1 ft8.1 fthh approx. 7.72 ftType:Area:Perimeter:6.10.4 cm7.08 cm7.64 cmhh = 5.2 cmType:Area:Perimeter:7.10.8 mm11.21 mm3 mmType:Area:Perimeter:8.11.1 yd8.18 yd6.44 ydhh = 4.7 ydType:Area:Perimeter:9.11 cm11 cm11 cmhh approx. 9.53 cmType:Area:Perimeter:math-sheet.comPage 1 / 1

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