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Ex 5.3, 7 - Chapter 5 Class 10 Arithmetic Progressions
Last updated at April 16, 2024 by Teachoo
Determining AP and finding sum
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
- Finding number of terms given s
- Given nth term finding s
- Statement questions - Sum of n terms
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Determining AP and finding sum
Transcript
Ex 5.3, 7 Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149. Given 22nd term = a22 = 149 Common difference = d = 7 We know that an = a + (n – 1) d Putting n = 22 , d = 7 , an = 149 149 = a + (22 – 1) × 7 149 = a + 21 × 7 149 = a + 147 149 = a + 147 149 – 147 = a 2 = a a = 2 Now, we need to find sum of first 22 terms And we are given a22 = 149 So, last term = l = 149 We use the formula Sn = 𝒏/𝟐 [ a + l ] Putting a = 2, n = 22, l = 149 = 22/2 [2 + 149] = 11 ×151 = 1661 Hence, Sum of first 22 terms is 1661
