Areas of Plane Figures between Parallel Lines

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Grade 11 · Term 1

Key points to revise

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About O/L Mathematics: O/L Mathematics covers number systems, algebra, geometry, trigonometry, and statistics across Grade 10 and 11.

• Area of a Trapezium:
• Formula: Area = (1/2) * (a + b) * h
• Where: a and b are the lengths of the two parallel sides (bases), and h is the perpendicular distance between them (height)
• Alternative: Area = (mid-segment length) * h, where mid-segment = (a + b)/2
• Area of a Parallelogram:

Must know

• Read the question carefully: Identify the shape(s) involved. Look for keywords like "trapezium," "parallelogram," "parallel lines," "perpendicular distance," "mid-segment." Draw a rough diagram if one is not provided
• Always state the formula: Before substituting numbers, write down the formula (e.g., Area = (1/2) * (a+b) * h). This shows the examiner your method and can earn you partial marks even if you make a calculation error
• Check units: Ensure all lengths are in the same unit before calculating. The final area should be in square units (e.g., cm², m²)
• Look for hidden parallel lines: In complex diagrams, parallel lines may not be explicitly marked. Look for arrows, right angles, or statements like "AB is parallel to CD." Use these to identify the height

Source: Idasara knowledge pack — english/OL_11/mathematics v16, short_notes: Lesson 08 - Areas of Plane Figures between Parallel Lines

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