Geometric Progressions

Where this fits in the syllabus

Grade 11 · Term 2

Key points to revise

Revise Geometric Progressions 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.

• General Term (nth term) of a GP:
• Common Ratio:
• Sum of First n Terms (when r = 1):
• Sum of First n Terms (when r != 1):
• Sum to Infinity (only when |r| < 1):

Must know

• Identify the type: Read the problem carefully. If it says "geometric progression" or "terms are multiplied by a constant", use GP formulas. If it says "common difference", it is an AP
• Write down given values: Always list a, r, n, Tn, Sn, etc., as given in the problem. This helps in selecting the correct formula
• Check r before using sum formulas: For Sn, if r=1, use Sn = n*a. For Sinfinity, ensure |r| < 1
• Use the division trick for two terms: If you know two terms of a GP, divide the larger term number by the smaller term number to find r^(difference in indices). This avoids solving simultaneous equations directly

Source: Idasara knowledge pack — english/OL_11/mathematics v16, short_notes: Lesson 16 - Geometric Progressions

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