8.1 Non-right Triangles: Law of Sines

The Law of Sines is a powerful tool for solving non-right triangles. It lets us find missing sides and angles when we don't have enough info for regular trig ratios. This law opens up a whole new world of triangle problem-solving.

We can use the Law of Sines to tackle real-world problems involving distances and angles. It's super handy for things like surveying, navigation, and even figuring out how tall buildings are. Pretty cool stuff!

Law of Sines and Its Applications

Law of Sines for non-right triangles

Top images from around the web for Law of Sines for non-right triangles

• 

  Non-right Triangles: Law of Sines | Algebra and Trigonometry View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines – Algebra and Trigonometry OpenStax View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines | Precalculus View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines | Algebra and Trigonometry View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines – Algebra and Trigonometry OpenStax View original

  Is this image relevant?

1 of 3

Top images from around the web for Law of Sines for non-right triangles

• 

  Non-right Triangles: Law of Sines | Algebra and Trigonometry View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines – Algebra and Trigonometry OpenStax View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines | Precalculus View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines | Algebra and Trigonometry View original

  Is this image relevant?

• 

  Non-right Triangles: Law of Sines – Algebra and Trigonometry OpenStax View original

  Is this image relevant?

1 of 3

• States the ratio of the sine of an angle to the length of the opposite side is constant for all three angles and sides in a triangle ABC: $\frac{\sin A}{a} = \frac{\sin B}{b} = \frac{\sin C}{c}$
• Applies to all triangles, including oblique triangles
• Solve non-right triangles using Law of Sines when given:
  • One angle measure and its opposite side length (AAS or ASA)
  • Measures of two angles (AAA)
  • Lengths of two sides and measure of a non-included angle (SSA)
• AAS or ASA solution steps:
  • Find the ratio $\frac{\sin A}{a}$ using given angle and side
  • Solve for unknown side lengths using this ratio
  • If needed, find remaining angle using known angles
• AAA solution steps:
  • Set up equation with unknown side lengths using Law of Sines
  • Solve for one side length
  • Find remaining side lengths using ratio $\frac{\sin A}{a}$
• SSA may have zero, one, or two possible triangles (ambiguous case):
  • Find angle opposite known non-included side using Law of Sines
  • Two possible triangles if angle is acute
  • One possible triangle if angle is right
  • No possible triangles if angle is obtuse or side opposite known angle is shorter than known side adjacent to angle

Area calculation with sine function

• Calculate area of non-right triangle using formula: $Area = \frac{1}{2}ab\sin C$
  • $a$ and $b$ are lengths of any two sides
  • $C$ is angle between chosen sides
• Area calculation steps:
  • Identify two known side lengths and angle between them
  • Substitute values into formula
  • Simplify expression to find area

Real-world applications of Law of Sines

• Identify given information in problem and determine if sufficient for Law of Sines
• Sketch triangle diagram, labeling known sides and angles
• Determine applicable case (AAS, ASA, AAA, or SSA)
• Apply appropriate steps to solve for unknown side lengths or angles
• If problem requires area, use formula $Area = \frac{1}{2}ab\sin C$ with known or calculated values
• Interpret results in problem context and provide clear answer with appropriate units (meters, square feet)

Triangle Properties and Trigonometric Relationships

• Triangle congruence: Two triangles are congruent if they have the same shape and size
• Triangle similarity: Two triangles are similar if they have the same shape but not necessarily the same size
• Trigonometric ratios: Relationships between sides and angles in right triangles, which form the basis for the sine function and other trigonometric functions
• Law of Sines extends these relationships to non-right triangles