JEE · Maths · Sequences & Series doubts
14 doubts found
What does “Arithmetic progression” actually mean in Sequences & Series, and why does it matter for JEE?
a sequence with a constant common difference d; the nth term is a+(n−1)d.
I keep getting “Arithmetic progression” questions wrong in Sequences & Series. What's the trap?
using the wrong count (n vs n−1) for the nth term.
What does “Geometric progression” actually mean in Sequences & Series, and why does it matter for JEE?
a sequence with a constant ratio r; the nth term is a·r^(n−1).
I keep getting “Geometric progression” questions wrong in Sequences & Series. What's the trap?
adding the ratio instead of multiplying by it.
What does “Infinite geometric series” actually mean in Sequences & Series, and why does it matter for JEE?
an infinite GP has a finite sum a/(1−r) only when |r| < 1.
I keep getting “Infinite geometric series” questions wrong in Sequences & Series. What's the trap?
applying the sum formula when |r| ≥ 1.
What is the difference between arithmetic progression and geometric progression?
An AP grows by adding a fixed number each step; a GP grows by multiplying by a fixed ratio each step.
What is the difference between finite series and infinite series?
A finite series always has a sum; an infinite series has one only if it converges (e.g. a GP with |r|<1).
When do I use aₙ = a + (n−1)d in Sequences & Series, and what does it mean?
nth term of an arithmetic progression.
When do I use aₙ = a·r^(n−1) in Sequences & Series, and what does it mean?
nth term of a geometric progression.
When do I use S∞ = a/(1−r) in Sequences & Series, and what does it mean?
sum of an infinite geometric series.
How is Sequences & Series tested in JEE, and what should I focus on?
Prioritise the core ideas: Arithmetic progression, Geometric progression, Infinite geometric series.
What are the most common mistakes students make in Sequences & Series?
the sum a/(1−r) exists only when |r|<1; otherwise the series diverges.
How do I revise Sequences & Series quickly before the exam?
One-page summary of Arithmetic progression, Geometric progression, Infinite geometric series, then timed previous-year questions.