Which term of the
Given AP is
Whose, first term, a = 20
Let nth term of the AP be the first negative term.
Then, we have to find the least value for which
⇒ an < 0
And we know, nth term of an AP = a + (n - 1)d
Where a and d are first term and common difference respectively.
⇒ a + ( n - 1 )d < 0
⇒ -3( n - 1 ) < -80
⇒ 3(n - 1) > 80
⇒ 3n - 3 > 80
⇒ 3n = 83
so, n will be least natural number greater than i.e.
i.e., 28th term is the first negative term of the given AP.
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