# 60 4 3 Practice Trigonometric Functions On The Unit Circle

## Introduction

Trigonometry is a branch of mathematics that deals with the relationships between the angles and sides of triangles. It has numerous applications in fields such as physics, engineering, and navigation. One fundamental concept in trigonometry is the unit circle, which allows us to understand the trigonometric functions in a graphical and geometric way. In this article, we will explore the practice of trigonometric functions on the unit circle, focusing on the 4-3 practice approach.

## Understanding Trigonometric Functions

### Sine Function

The sine function (sinθ) is one of the primary trigonometric functions. It represents the ratio of the length of the side opposite to an angle in a right triangle to the length of the hypotenuse. On the unit circle, the sine function corresponds to the y-coordinate of a point on the circle. As we move around the unit circle in a counter-clockwise direction, the sine function oscillates between -1 and 1.

### Cosine Function

The cosine function (cosθ) is another crucial trigonometric function. It represents the ratio of the length of the adjacent side to an angle in a right triangle to the length of the hypotenuse. On the unit circle, the cosine function corresponds to the x-coordinate of a point on the circle. Similar to the sine function, the cosine function also fluctuates between -1 and 1 as we move around the unit circle.

### Tangent Function

The tangent function (tanθ) is derived from the sine and cosine functions. It represents the ratio of the sine of an angle to its cosine. Mathematically, tanθ = sinθ / cosθ. On the unit circle, the tangent function can be found by dividing the y-coordinate (sine) by the x-coordinate (cosine) of a point on the circle. The tangent function is undefined at certain angles where the cosine is zero.

## The Unit Circle

### Definition

The unit circle is a circle with a radius of 1 unit, centered at the origin of a Cartesian coordinate system. It is a powerful tool in trigonometry that allows us to visualize and understand the relationships between angles and trigonometric functions. By placing the unit circle in the coordinate plane, we can associate each point on the circle with a specific angle and its corresponding trigonometric values.

Quadrantal angles are angles that lie on the axes of the unit circle, specifically 0°, 90°, 180°, and 270°. These angles have distinct trigonometric values. For example, at 0°, the sine function is 0, while the cosine function is 1. At 90°, the sine function is 1, and the cosine function is 0. Similarly, at 180°, the sine function is 0, and the cosine function is -1. Finally, at 270°, the sine function is -1, and the cosine function is 0.

In addition to degrees, angles on the unit circle can also be measured in radians. Radians are a unit of angular measurement that relates the length of an arc on a circle to the radius. One revolution around the unit circle is equal to 2π radians, or approximately 6.28 radians. The radian measure allows for more precise calculations and is commonly used in calculus and advanced trigonometry.

## The 4-3 Practice Approach

### Explanation

The 4-3 practice approach is a method used to determine the values of trigonometric functions at various angles on the unit circle. It involves identifying the reference angle, determining the quadrant, and applying the appropriate sign based on the quadrant. This approach simplifies the process of finding the trigonometric values for angles outside the quadrantal angles.

### Step 1: Determine the Reference Angle

The reference angle is the acute angle formed between the terminal side of an angle and the x-axis. To find the reference angle, we measure the angle from the positive x-axis to the terminal side and disregard any full revolutions around the unit circle. The reference angle is always positive and lies within the range of 0° to 90° (or 0 to π/2 radians).

### Step 2: Determine the Quadrant

After finding the reference angle, we determine the quadrant in which the angle lies. The quadrant is determined by the signs of the x and y coordinates of the point on the unit circle corresponding to the angle. Each quadrant has specific characteristics that affect the signs of the trigonometric functions.

### Step 3: Apply the Signs

Once the quadrant is determined, we apply the appropriate sign to the trigonometric functions based on the quadrant. The signs are as follows:

• Quadrant I: All trigonometric functions are positive.
• Quadrant II: Only the sine function is positive.
• Quadrant III: Only the tangent function is positive.
• Quadrant IV: Only the cosine function is positive.

## Example

### Angle: 150°

Step 1: Determine the Reference Angle

The reference angle for 150° is 30°. This is because the angle formed between the terminal side and the x-axis is 150° - 360° (1 full revolution) = -210°. Since the reference angle is always positive, we take the absolute value of -210°, which gives us 210°. Since 210° is greater than 180°, we subtract it from 360° to find the reference angle: 360° - 210° = 150°.