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Ex 8.2, 2
Last updated at June 9, 2026 by Teachoo
Class 9
Chapter 8 - Predicting What Comes Next: Exploring Sequences & Progress
- Definition
- Explicit Rule for a Sequence
- Recursive Rule for a Sequence
- Virahānka–Fibonacci sequence
- Exercise Set 8.1
- Arithmetic Progressions
- Visualising an AP
- Sum of the First n Natural Numbers
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Exercise Set 8.2
- Geometric Progressions
- Fractals as a GP Sequence
- Visualising a GP
- Exercise Set 8.3
- End-of-Chapter Exercises
Transcript
Ex 8.2, 2 Which term of the AP 21, 18, 15,… is -81 ? Also, is 0 a term of this AP? Give reasons for your answer. Given AP 21, 18, 15, ……. Here, First term = a = 21 Common difference = d = 18 – 21 = –3 We need to find which term is – 81. So, an = – 81 We need to find n Using nth term formula an = a + (n – 1) d Putting values –81 = 21 + (n – 1) × (–3) –81 = 21 + n × – 3 – 1 × –3 –81 = 21 – 3n + 3 –81 = 24 – 3n 3n = 24 + 81 3n = 105 n = 105/3 n = 35 Therefore, the 35th term of given AP is –81 Now, we are asked Also, is 0 a term of this AP? Let’s put an = 0, and find n Now, an = a + (n – 1)d Putting a = 21, d = –3, an = 0 0 = 21 + (n – 1) (–3) 0 = 21 + n × –3 – 1 × –3 0 = 21 – 3n + 3 0 = 24 – 3n 3n = 24 n = 24/3 n = 8 Therefore, 8th term of given AP is 0
