Question

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

Answer 1

Here

a=121. d=(117-121)=-4

AND Nth Term is negative so 

Tn<0

a+(n-1)d<0

121+(n-1)(-4)<0

121<(n-1)4

121/4<n-1

(121/4)+1<n

n>125/4

n>34.something

so number that greater then 34 and smallest is 35 ..

Thus 35th Term is it's First NEGATIVE TERM..