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2.1. Primary Trigonometric Ratios
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Good morning, class! Today we’re diving into our first topic on trigonometry: the right-angled triangle. Can anyone tell me what a right-angled triangle is?
Is it a triangle with one angle equal to 90 degrees?
Exactly! In a right-angled triangle, one angle is 90 degrees. Now, let's learn about its sides. We call the longest side opposite the right angle the hypotenuse. Can someone tell me the other two sides?
There’s the opposite and the adjacent sides!
Correct! The opposite is opposite from our angle of interest, denoted as 𝜃, and the adjacent side is next to 𝜃, excluding the hypotenuse. Remember this terminology as we explore trigonometric ratios deeper.
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"Now that we know the sides, let’s dive into the trigonometric ratios: sine, cosine, and tangent. These ratios illustrate the relationship between an angle and the lengths of the sides of the triangle. Let's break it down.
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Create a free account"Moving on, we have reciprocal trigonometric ratios, which are cosecant, secant, and cotangent. Let’s list them out based on our primary ratios:
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Create a free account"Let’s apply what we've learned. To find unknown sides, we can rearrange our ratios. For example, if we need to find the opposite side, we can use:
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Create a free accountLet’s wrap up with the application. When we're solving real-world problems, we follow a systematic approach. What are the steps?
Identify known sides or angles, choose the appropriate ratio, write the equation and solve!
Amazing! Always remember to verify your answer aligns with triangle properties. Let’s look at an example problem to connect these concepts!
Can we do a problem together?
Absolutely! We'll work through finding an unknown side together.
Overview
Short Summary
This section introduces the primary trigonometric ratios and their definitions related to right-angled triangles.
Medium Summary
In this section, we define the three primary trigonometric ratios: sine, cosine, and tangent, as well as their reciprocal functions. We provide explanations on how these ratios are derived from the sides of a right-angled triangle and their applications in solving problems involving angles and sides.
Detailed Summary
Primary Trigonometric Ratios
Trigonometry focuses on the relationships between angles and sides in right-angled triangles. The three primary trigonometric ratios are sine (sin), cosine (cos), and tangent (tan), defined as follows:
- sin𝜃 = (Opposite side) / (Hypotenuse)
- cos𝜃 = (Adjacent side) / (Hypotenuse)
- tan𝜃 = (Opposite side) / (Adjacent side)
These ratios apply to angles between 0° and 90° in a right triangle. Reciprocal ratios include cosecant (csc), secant (sec), and cotangent (cot), defined in relation to the primary ratios.
Understanding these ratios is fundamental to solving problems in trigonometry, especially using the inverse functions to find unknown angles when two sides of a triangle are known. Additionally, the Pythagorean theorem establishes a fundamental identity that links these ratios: sin²𝜃 + cos²𝜃 = 1. This section sets the stage for applying these concepts in practical problem-solving.
Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Sine Ratio: Represents the ratio of the opposite side over the hypotenuse.
Cosine Ratio: Represents the ratio of the adjacent side over the hypotenuse.
Tangent Ratio: Represents the ratio of the opposite side over the adjacent side.
Reciprocal Ratios: Include cosecant, secant, and cotangent as inversions of the primary ratios.
Pythagorean Identity: Links sin²𝜃 and cos²𝜃 to equal 1, forming a fundamental relationship.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
Example 1: Given a triangle with a hypotenuse of 10 cm and angle 𝜃 = 30°, find the opposite side using sin: Opposite = 10 × sin(30°) = 5 cm.
Example 2: Given a triangle with an adjacent side of 7 cm and angle 𝜃 = 45°, find the hypotenuse using cos: Hypotenuse = 7 / cos(45°) = 7√2 ≈ 9.9 cm.
Memory Aids
Interactive tools to help you remember key concepts
Stories
Memory Tools
Flash Cards
Glossary
Hypotenuse
The longest side of a right-angled triangle, opposite the right angle.
Opposite Side
The side opposite to the angle of interest (𝜃) in a triangle.
Adjacent Side
The side that is next to the angle of interest (𝜃) excluding the hypotenuse.
Sine (sin)
A trigonometric ratio defined as the ratio of the opposite side to the hypotenuse.
Cosine (cos)
A trigonometric ratio defined as the ratio of the adjacent side to the hypotenuse.
Tangent (tan)
A trigonometric ratio defined as the ratio of the opposite side to the adjacent side.
Cosecant (csc)
The reciprocal of sine, defined as 1/sin𝜃.
Secant (sec)
The reciprocal of cosine, defined as 1/cos𝜃.
Cotangent (cot)
The reciprocal of tangent, defined as 1/tan𝜃.
Pythagorean Identity
An identity relating sine and cosine: sin²𝜃 + cos²𝜃 = 1.