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Understanding SOH-CAH-TOA in Trigonometry

Apr 24, 2025

Lecture Notes: SOH-CAH-TOA

Introduction

  • SOH-CAH-TOA is a mnemonic device used to remember the basic trigonometric ratios which are essential for solving missing sides and angles in a right triangle.
  • It is derived from the AA Similarity Postulate which states that the ratios of the lengths of two sides of similar right triangles are equal.

Definition of SOH-CAH-TOA

  • SOH: Sin(θ) = Opposite / Hypotenuse
  • CAH: Cos(θ) = Adjacent / Hypotenuse
  • TOA: Tan(θ) = Opposite / Adjacent

Importance

  • These trigonometric ratios hold true for all right triangles, irrespective of their size.
  • They are crucial for determining missing measurements in triangles.

Remembering Trig Functions

  • Mnemonic Sayings:
    • "Some Of Her Children Are Having Trouble Over Algebra"
    • "Oscar Had A Heap Of Apples"
  • Triangle Sides Labeling:
    • Opposite Leg: The side opposite the acute angle.
    • Adjacent Leg: The side next to the acute angle but not the hypotenuse.
    • Hypotenuse: The longest side, opposite the right angle.

Application

  • Used to solve for unknown sides or angles in right triangles using the trigonometric ratios.
  • Inverse Trig Ratios are used to find missing angles when two side lengths are known.

Common Questions

  • Applicability: SOH-CAH-TOA is only applicable to right triangles.
  • Usage: Utilized when two sides of a right triangle are known and the third side or angles need to be calculated.
  • Hypotenuse Position: Opposite to the 90-degree angle and the longest side.
  • Adjacent Side: The side touching the angle but not the hypotenuse.
  • Solving a Right Triangle: Involves finding all missing sides and angles using trig ratios, triangle sum theorem, and/or Pythagorean theorem.

Video Lesson Highlights

  • Duration: 1 hr 34 min
  • Breakdown:
    • Intro to Trigonometric Ratios
    • Understanding SOH-CAH-TOA
    • Finding Trig Ratios for Acute Angles
    • Completing Tables Using SOH-CAH-TOA
    • Solving Angles with a Calculator
    • Solving Right Triangles
    • Application in Word Problems
    • Finding Unknowns Using SOH-CAH-TOA

Additional Resources

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  • Practice Problems and Chapter Tests provide additional learning support.

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