erplex
  • Lessons
  • Problems
  • Speed Run
  • Practice Tests
  • Skill Checklist
  • Review Videos
  • Landing Page
  • Sign Up
  • Login
  • erplex
    IB Math AASL
    /
    Sequences & Series
    /

    Video

    Video Reviews

    Watch comprehensive video reviews for most units, designed for final exam preparation. Each video includes integrated problems you can solve alongside detailed solutions.

    Not your average video:

    Interactive Problems: Solve problems alongside the video with step-by-step guidance and detailed solutions.

    Exam Preparation: Complete unit reviews designed for final exam preparation with all key concepts covered systematically.

    Expert Teaching: High-quality instruction from Perplex co-founder James Mullen with clear explanations, worked examples, and exam tips.

    Not your average video:

    Interactive Problems: Solve problems alongside the video with step-by-step guidance and detailed solutions.

    Exam Preparation: Complete unit reviews designed for final exam preparation with all key concepts covered systematically.

    Expert Teaching: High-quality instruction from Perplex co-founder James Mullen with clear explanations, worked examples, and exam tips.

    Sequences & Series

    Video Reviews

    Watch comprehensive video reviews for Sequences & Series, designed for final exam preparation. Each video includes integrated problems you can solve alongside detailed solutions.

    Not your average video:

    Interactive Problems: Solve problems alongside the video with step-by-step guidance and detailed solutions.

    Exam Preparation: Complete unit reviews designed for final exam preparation with all key concepts covered systematically.

    Expert Teaching: High-quality instruction from Perplex co-founder James Mullen with clear explanations, worked examples, and exam tips.

    Not your average video:

    Interactive Problems: Solve problems alongside the video with step-by-step guidance and detailed solutions.

    Exam Preparation: Complete unit reviews designed for final exam preparation with all key concepts covered systematically.

    Expert Teaching: High-quality instruction from Perplex co-founder James Mullen with clear explanations, worked examples, and exam tips.

    SequencesSeriesPaper 1 ProblemsFinancePaper 2 Problems

    The video will automatically pause when it reaches a problem.

    Convergence

    SL AA 1.8

    A geometric series is said to converge if S∞​ is finite - which means ∣r∣<1⇔−1<r<1.


    Example

    A geometric sequence has u1​=8 and u4​=2k+1. For what value(s) of k does the corresponding geometric series converge?


    We have

    u4​=u1​r3=8⋅r3=2k+1⇒r3=82k+1​

    Now if −1<r<1, then −1<r3<1:

    −1<82k+1​<1
    −8<2k+1<8
    −29​<k<27​

    Convergence

    SL AA 1.8

    A geometric series is said to converge if S∞​ is finite - which means ∣r∣<1⇔−1<r<1.


    Example

    A geometric sequence has u1​=8 and u4​=2k+1. For what value(s) of k does the corresponding geometric series converge?


    We have

    u4​=u1​r3=8⋅r3=2k+1⇒r3=82k+1​

    Now if −1<r<1, then −1<r3<1:

    −1<82k+1​<1
    −8<2k+1<8
    −29​<k<27​
    SequencesSeriesPaper 1 ProblemsFinancePaper 2 Problems