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sum of how many term of series

6+12+18+24+… is 1800?
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sun of n terms of AP = N/2{2a+(n-1)*d} where a= first term .d=common difference ,n= number of terms

now put values in the formula a=6, d=6 , n=?,sum=1800

N/2{2*6+(n-1)*6}=1800

$n^{2}+n-600=0$

solving the quadratic equation you will get 24 terms so answer is 24
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