- A17th
- B20th
- C18th
- D19th
Step-by-Step Solution
. Set → → → . Check: . Stopping at and answering 18th is the usual slip.
Answer: D) 19th
Which term of the AP 5, 2, -1, -4, … is -49?
Class 10Arithmetic ProgressionsAlgebra — Sequences
Key idea: n-th term formula
**aₙ = a + (n − 1)d**
Where a is the first term, d is the common difference, n is the position.
**Why**: a₁ = a; a₂ = a + d; a₃ = a + 2d; … aₙ = a + (n − 1)d. Each step adds another d.
**Example**: AP 3, 7, 11, 15, …. Find the 20th term.
a = 3, d = 4. a₂₀ = 3 + 19·4 = 79.
**Reverse use**: 'In the AP 5, 11, 17, …, which term is 89?' a + (n−1)d = 89 → 5 + 6(n−1) = 89 → n = 15.
Where a is the first term, d is the common difference, n is the position.
**Why**: a₁ = a; a₂ = a + d; a₃ = a + 2d; … aₙ = a + (n − 1)d. Each step adds another d.
**Example**: AP 3, 7, 11, 15, …. Find the 20th term.
a = 3, d = 4. a₂₀ = 3 + 19·4 = 79.
**Reverse use**: 'In the AP 5, 11, 17, …, which term is 89?' a + (n−1)d = 89 → 5 + 6(n−1) = 89 → n = 15.
Master this chapter in 30 minutes a day.
Don't just memorise the answer — build a daily practice habit.
Practice 5 Similar Questions Free →All Arithmetic Progressions practice questions
More Class 10 Arithmetic Progressions practice
In the AP 60, 56, 52, 48, …, which term is the first negative term?What is the value of the first negative term of the AP 121, 117, 113, 109, …?The 6th term of an AP is 19 and its 14th term is 43. Find its 25th term.A student computed the 12th term of the AP 4, 10, 16, … as a_12 = 4 + 12 × 6 = 76. What…Find the sum of the first 18 terms of the AP 7, 11, 15, 19, ….