Geometry & Mensuration • Topic 4 of 5

2D Mensuration

Master the plane-figure formulas: rectangle lb, square a^2, triangle (1/2)bh (or Heron's for three sides), parallelogram base x height, trapezium (1/2)(sum of parallel sides) x height, circle pi r^2 with circumference 2 pi r. Use pi = 22/7 when the radius is a multiple of 7. For a path/border, subtract the inner area from the outer.

✅ Solved examples

1. Area of a rectangle 12 by 8?
12 x 8 = 96.
2. Area of a circle of radius 7 (pi = 22/7)?
22/7 x 49 = 154.
3. Area of a triangle base 10, height 6?
(1/2) x 10 x 6 = 30.
4. Area of a trapezium with parallel sides 8 and 12, height 5?
(1/2)(8+12) x 5 = 50.

✏️ Practice — try these, take hints as needed

1. Area of a square of side 9?
side^2.
—
—
81
2. Circumference of circle r = 14 (pi 22/7)?
2 pi r.
2 x 22/7 x 14.
—
88
3. Triangle base 16, height 5?
(1/2)bh.
—
—
40
4. Area of circle r = 21 (pi 22/7)?
pi r^2.
22/7 x 441.
—
1386
5. Trapezium parallel 6 and 10, height 4?
(1/2)(16)(4).
—
—
32

📝 Topic test — 8 questions

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