Right Triangle Terminology
Hypotenuse, opposite and adjacent sides relative to an angle.
Key idea
Hypotenuse, opposite and adjacent sides relative to an angle.
In depth
In a right triangle, the hypotenuse is opposite the right angle and is the longest side. For a chosen acute angle θ, the opposite side faces it and the adjacent side touches it. The labels change when you change the reference angle.
Worked example
In a 3-4-5 triangle, for the angle opposite the side 3, opposite = 3, adjacent = 4, hypotenuse = 5.
Real-world uses
- Labelling sides correctly when measuring a ramp, a ladder or a slope in construction
Common mistake
Labelling opposite and adjacent relative to the wrong angle.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Right Triangle Terminology?
Hypotenuse, opposite and adjacent sides relative to an angle. It is a topic at the beginner level in Trigonometry.
Where is Right Triangle Terminology used in real life?
Real-world examples: Labelling sides correctly when measuring a ramp, a ladder or a slope in construction.
What should I learn before Right Triangle Terminology?
Make sure you are comfortable with Converting Degrees and Radians, the previous topic in Trigonometry.
What is a common mistake with Right Triangle Terminology?
Labelling opposite and adjacent relative to the wrong angle.
How can I practise Right Triangle Terminology?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Right Triangle Terminology?
Move on to Sine Ratio next.
Related beginner topics in Trigonometry
- Angle Measure: Degrees – A full turn is 360°; angles measure rotation.
- SOH-CAH-TOA – Memory aid for the three basic ratios.