Mathematics · Arithmetic Progressions · NCERT Examples
Example 11
A complete, independently verified solution for NCERT Example 11.
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Mathematics · Chapter 5 · NCERT Examples
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NCERT Example
Example 11
Find the sum of the first 22 terms of 8,3,−2,…
Solution
Board-exam working:
Here a=8,d=3−8=−5,n=22.
S₂₂=22/2[2×8+(22−1)(−5)]=11[16−105]=11(−89)=−979.
The last term is a₂₂=8+21(−5)=−97, and 22/2(8−97)=11(−89)=−979, confirming the sum.
Final answer
−979.