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Question:

Which term of the AP: 121, 117, 113,... is its first negative term? [Hint: Find n for an < 0]

Solution:

Given A.P is121,117,113...a=121andd=117−1;21=−4an=a+(n−1;)d=121+(n−1;)(−4)=121−4n+4=125−4nWe have find the first term of this A.P.Thereforean<0125−4n<0124<4nn>1254n>31.25n=32