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Question
Find the number of terms of the AP 18, `15``1/2` 13, ….., `49``1/2` and find the sum of all its terms n?
Solution
The AP is given as `18 , 15``1/2-18=-2``1/2`and the last term of the AP =`-49``1/2`
Let the AP has n terms.
∴an = a + (n − 1) d
`rArr -49``1/2=18-(n-1)xx2``1/2rArr-99/2=18-5/2(n-1)`
`rArr5(n-1)=135`
`thereforen=27+1=28`
Thus, the given AP has 28 terms.
Now, the sum of all the terms (Sn) is given by,
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