Surface Area of Solids

Where this fits in the syllabus

Grade 11 · Term 1

Key points to revise

Revise Surface Area of Solids fast with concise, exam-ready key points

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

• For prisms and cylinders: Lateral surface area = perimeter of base * height
• For pyramids and cones: Lateral surface area = (1/2) * perimeter of base * slant height
• Slant height (l) is the distance from the vertex to the edge of the base along the lateral surface. It is not the vertical height (h). For a cone: l² = r² + h². For a pyramid: l² = (half base width)² + h²
• Always check if the solid is "closed" (includes all faces) or "open" (missing some faces, e.g., a cylindrical tank without a lid)

Must know

• Memorize all formulas: Write them on a revision card. Practice recalling them without looking
• Draw the net: If confused, sketch the net of the solid. This helps visualize all faces and avoid missing any
• Check for "open" or "closed": Exam problems often specify "without a lid" or "open at one end". Adjust the formula accordingly (e.g., cylinder without top: SA = πr² + 2πrh)
• Use π = 22/7 when numbers are multiples of 7: This simplifies calculations. If numbers are not multiples of 7, use π = 3.14 or leave answer in terms of π if instructed

Source: Idasara knowledge pack — english/OL_11/mathematics v16, short_notes: Lesson 04 - Surface Area of Solids

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