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Example 12 - Chapter 5 Class 10 Arithmetic Progressions
Last updated at April 16, 2024 by Teachoo
Finding number of terms given s
Chapter 5 Class 10 Arithmetic Progressions
Concept wise
- Checking if AP or not and finding a, d
- Finding nth term
- Finding n
- Finding AP
- Finding nth term from end
- Divisible/ multiples
- Statement questions - nth term
- Finding sum of n terms
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Finding number of terms given s
- Given nth term finding s
- Statement questions - Sum of n terms
- Determining AP and finding sum
Transcript
Example 12 If the sum of the first 14 terms of an AP is 1050 and its first term is 10, find the 20th term. Here, Sum of the first 14 terms of an AP is 1050. So, S14 = 1050 Also, a = 10 & n = 14 We know that Sum = 𝒏/𝟐[𝟐𝒂+(𝒏−𝟏)𝒅] Putting values 1050 = 14/2[2×(10)+(14−1)𝑑] 1050 = 7[20+13𝑑] 1050/7=20+13𝑑 150 = 20 + 13d 13d = 150 – 20 13d = 130 d = 10 We have to find 20th term We use the formula an = a + (n – 1) d Putting a = 10 , d = 10 , n = 20 a20 = 10 + (20 – 1) 10 a20 = 10 + (19 )×10 a20 = 10 + 190 a20 = 200
