### About Geometric Sequences and Series:

A geometric sequence, which is also known as a geometric progression is a sequence in which each term after the first is obtained by multiplying the preceding term by a fixed nonzero real number. The fixed nonzero real number is known as the common ratio.

Test Objectives
• Demonstrate the ability to find the common ratio
• Demonstrate the ability to find the nth term of a geometric sequence
• Demonstrate the ability to evaluate a geometric series
Geometric Sequences and Series Practice Test:

#1:

Instructions: Find the common ratio and the explicit formula.

$$a)\hspace{.2em}1, 4, 16, 64,...$$

Instructions: Find the term named and the explicit formula.

$$b)\hspace{.2em}2, -6, 18, -54,...$$ $$\text{Find}: a_{11}, a_{n}$$

#2:

Instructions: Find the term named and the explicit formula.

$$a)\hspace{.2em}a_{4}=27, a_{1}=1$$ $$\text{Find}: a_{12}, a_{n}$$

$$b)\hspace{.2em}a_{1}=4, a_{6}=-972$$ $$\text{Find}: a_{11}, a_{n}$$

#3:

Instructions: Find the term named and the explicit formula.

$$a)\hspace{.2em}a_{4}=-16, a_{5}=32$$ $$\text{Find}: a_{10}, a_{n}$$

$$b)\hspace{.2em}a_{2}=-2, a_{3}=-4$$ $$\text{Find}: a_{9}, a_{n}$$

#4:

Instructions: Evaluate each geometric series.

$$a)\hspace{.2em}\sum_{k=1}^{8}-3 \cdot 2^{k - 1}$$

$$b)\hspace{.2em}\sum_{i=1}^{8}(-5)^{i - 1}$$

#5:

Instructions: Evaluate each geometric series.

$$a)\hspace{.2em}\sum_{i=1}^{9}4 \cdot 3^{i - 1}$$

$$b)\hspace{.2em}\sum_{m=1}^{\infty}-2 \cdot \left(\frac{1}{2}\right)^{m - 1}$$

Written Solutions:

#1:

Solutions:

$$a)\hspace{.2em}r=4$$ $$a_{n}=4^{n - 1}$$

$$b)\hspace{.2em}a_{11}=118{,}098$$ $$a_{n}=2 \cdot (-3)^{n - 1}$$

#2:

Solutions:

$$a)\hspace{.2em}r=3$$ $$a_{12}=177{,}147$$ $$a_{n}=3^{n - 1}$$

$$b)\hspace{.2em}r=-3$$ $$a_{11}=236{,}196$$ $$a_{n}=4 \cdot (-3)^{n - 1}$$

#3:

Solutions:

$$a)\hspace{.2em}r=-2$$ $$a_{10}=-1024$$ $$a_{n}=2 \cdot (-2)^{n - 1}$$

$$b)\hspace{.2em}r=2$$ $$a_{9}=-256$$ $$a_{n}=-2^{n - 1}$$

#4:

Solutions:

$$a)\hspace{.2em}-765$$

$$b)\hspace{.2em}-65{,}104$$

#5:

Solutions:

$$a)\hspace{.2em}39{,}364$$

$$b)\hspace{.2em}-4$$