Question

Choose the correct answer in each of the following questions:

Which term of the AP 72, 63, 54, ... is 0?

(a) 8th (b) 9th (c) 10th (d) 11th

Answer 1

The given AP is 72, 63, 54, ... .

Here, a = 72 and d = 63 − 72 = −9

Suppose n^th term of the given AP is 0. Then,

$$\begin{gathered} a_n=0 \\ \Rightarrow 72+\left(n-1\right)\times \left(-9\right)=0\left[a_n=a+\left(n-1\right)d\right] \\ \Rightarrow -9n+81=0 \\ \Rightarrow n=\frac{81}{9}=9 \end{gathered}$$

Thus, the 9th term of the given AP is 0.

Hence, the correct answer is option B.