# Lesson 11

### Lesson Narrative

The goal of this lesson is for students to encounter several situations where it makes sense to find the sum of a sequence, defined here as adding up the value of the terms of the sequence. At this point, the number of terms students need to sum is kept short since the summing is by hand. In a future unit students use polynomial identities to develop a formula to sum the first $$n$$ terms of any geometric sequence.

The main activities in this lesson are meant to be relatively unscaffolded, giving students the opportunity to make sense of the problems using the tools they have worked with throughout this unit, such as tables, graphs, and equations (MP1).

### Learning Goals

Teacher Facing

• Calculate the sum of a simple geometric sequence describing a situation without the use of a formula.

### Student Facing

• Let’s look at sequences and the sum of their terms.

### Required Preparation

Provide 1 piece of blank paper and 1 pair of scissors for every 4 students to act out the situation in the activity Paper Trail.

### Student Facing

• I can determine the sum of a sequence representing a situation.

Building On