# Lesson 7

Finding Unknown Coordinates on a Circle

### Lesson Narrative

In this lesson, students are building skills that will help them in mathematical modeling (MP4). They learn to use the unit circle as a starting point for thinking about circular motion and then scale their results appropriately to model clocks of different sizes or scale and translate them to model a Ferris wheel whose center is not at $$(0,0)$$. Students find the coordinates of points on these circles algebraically and then consider what they represent in context. They also consider the difference between approximating the coordinates and representing them exactly as expressions using cosine and sine. These ideas are developed further throughout the unit, leading eventually to the notions of amplitude and midline of trigonometric functions and using these functions for modeling different types of periodic relationships.

Technology isn’t required for this lesson, but there are opportunities for students to choose to use appropriate technology to solve problems (MP5) and we recommend making technology available.

### Learning Goals

Teacher Facing

• Use sine and cosine to find coordinates of points on a circle in all 4 quadrants.

### Student Facing

• Let’s find coordinates on a circle.

### Required Preparation

It will be helpful for students to have access to scientific calculators if they choose to compute approximate trigonometric values to help give meaning to their answers in context.

It may be helpful for some students to have extra copies of the gridded clock faces in the activity “Clock Coordinates.” Consider printing and making extras available using the Blackline Master.

Devices are required for the digital version of the activity “Around a Ferris Wheel.”

### Student Facing

• I can use cosine and sine to figure out information about points rotating in circles.

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