Table of contents
- 0. Fundamental Concepts of Algebra3h 32m
- 1. Equations and Inequalities3h 27m
- 2. Graphs1h 43m
- 3. Functions & Graphs2h 17m
- 4. Polynomial Functions1h 54m
- 5. Rational Functions1h 23m
- 6. Exponential and Logarithmic Functions2h 28m
- 7. Measuring Angles40m
- 8. Trigonometric Functions on Right Triangles2h 5m
- 9. Unit Circle1h 19m
- 10. Graphing Trigonometric Functions1h 19m
- 11. Inverse Trigonometric Functions and Basic Trig Equations1h 41m
- 12. Trigonometric Identities 2h 34m
- 13. Non-Right Triangles1h 38m
- 14. Vectors2h 25m
- 15. Polar Equations2h 5m
- 16. Parametric Equations1h 6m
- 17. Graphing Complex Numbers1h 7m
- 18. Systems of Equations and Matrices3h 6m
- 19. Conic Sections2h 36m
- 20. Sequences, Series & Induction1h 15m
- 21. Combinatorics and Probability1h 45m
- 22. Limits & Continuity1h 49m
- 23. Intro to Derivatives & Area Under the Curve2h 9m
8. Trigonometric Functions on Right Triangles
Trigonometric Functions on Right Triangles
Struggling with Precalculus?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
Given the right triangle below, evaluate cosθ.

A
cosθ=178
B
cosθ=158
C
cosθ=1715
D
cosθ=815

1
Identify the sides of the right triangle: the side adjacent to angle θ is 15, the opposite side is 8, and the hypotenuse is 17.
Recall the definition of cosine for a right triangle: cos(θ) = adjacent/hypotenuse.
Substitute the known values into the cosine formula: cos(θ) = 15/17.
Verify the calculation by checking the Pythagorean theorem: 15^2 + 8^2 = 17^2, which confirms the side lengths are correct.
Conclude that the correct value of cos(θ) is 15/17.
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