In Exercises 1–8, solve each triangle. Round lengths of sides to the nearest tenth and angle measures to the nearest degree.
Table of contents
- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
7. Non-Right Triangles
Law of Cosines
Problem 1
Textbook Question
CONCEPT PREVIEW Assume a triangle ABC has standard labeling.
a. Determine whether SAA, ASA, SSA, SAS, or SSS is given.
b. Determine whether the law of sines or the law of cosines should be used to begin solving the triangle.
a, b, and C
Verified step by step guidance1
Identify the given parts of the triangle: sides \( a \) and \( b \), and angle \( C \). Since two sides and the included angle are given, this corresponds to the SAS (Side-Angle-Side) case.
Recall the definitions of the triangle congruence cases: SAA (two angles and a side), ASA (angle-side-angle), SSA (side-side-angle), SAS (side-angle-side), and SSS (side-side-side). Here, the angle \( C \) is between sides \( a \) and \( b \), confirming SAS.
For SAS, the Law of Cosines is the appropriate tool to use first because it relates two sides and the included angle to find the third side. The Law of Cosines formula is: \[ c^2 = a^2 + b^2 - 2ab \cos(C) \].
Use the Law of Cosines to find the unknown side \( c \) by substituting the known values of \( a \), \( b \), and \( C \) into the formula.
After finding side \( c \), you can use the Law of Sines or other methods to find the remaining angles or sides as needed.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Triangle Congruence Criteria (SAA, ASA, SSA, SAS, SSS)
These criteria describe how triangles can be determined or solved based on known sides and angles. SAA (or AAS) and ASA involve two angles and one side, SAS involves two sides and the included angle, SSS involves all three sides, and SSA involves two sides and a non-included angle, which can be ambiguous.
Recommended video:
Solving SAS & SSS Triangles
Law of Sines
The Law of Sines relates the ratios of sides to the sines of their opposite angles in any triangle. It is especially useful when two angles and one side (AAS or ASA) or two sides and a non-included angle (SSA) are known, allowing for the calculation of unknown sides or angles.
Recommended video:
Intro to Law of Sines
Law of Cosines
The Law of Cosines generalizes the Pythagorean theorem for any triangle, relating the lengths of sides to the cosine of an included angle. It is typically used when two sides and the included angle (SAS) or all three sides (SSS) are known, enabling the calculation of unknown sides or angles.
Recommended video:
Intro to Law of Cosines
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