Question

What is the value of the fourth term in a geometric sequence for which a1 = 30 and r = 1/2?.

Answer 1

$\bf n^{th}\textit{ term of a geometric sequence}\\\\ a_n=a_1\cdot r^{n-1}\qquad \begin{cases} n=n^{th}\ term\\ a_1=\textit{first term's value}\\ r=\textit{common ratio}\\ ----------\\ a_1=30\\ r=\frac{1}{2}\\ n=4 \end{cases}\implies a_4=30\left( \frac{1}{2} \right)^{4-1}$