Naming sides and basic ratios

Right-angled triangle relative to angle $θ\theta$ :

          θ
          o
         /|
        / |
       /  | adjacent
      /   |
     /    |
    o-----o
     opposite

Trigonometric ratios link an angle to side lengths. In a right-angled triangle, the side names depend on the chosen angle $θ\theta$ .

With $θ\theta$ at the top vertex and the right angle at the bottom-right corner:

the vertical side next to $θ\theta$ is the adjacent side
the sloping longest side is the hypotenuse
the bottom horizontal side across from $θ\theta$ is the opposite side

Step-by-step lessons covering Edexcel A Level Maths Trigonometric Ratios for A Level Maths. Each lesson breaks down 9.1 The Cosine Rule, 9.2 The Sine Rule, 9.3 Areas of Triangles, 9.4 Solving Triangle Problems, 9.5 Graphs of Sine, Cosine and Tangent, and 9.6 Transforming Trigonometric Graphs, then works through exam-style questions in Paper 1, Paper 2 and Paper 3 format. Build fluency with the core pure algebra and calculus toolkit early, since almost every mechanics and statistics topic on the course depends on it.

Naming sides and basic ratios

Right-angled triangle relative to angle $θ\theta$ :

          θ
          o
         /|
        / |
       /  | adjacent
      /   |
     /    |
    o-----o
     opposite

Trigonometric ratios link an angle to side lengths. In a right-angled triangle, the side names depend on the chosen angle $θ\theta$ .

With $θ\theta$ at the top vertex and the right angle at the bottom-right corner:

the vertical side next to $θ\theta$ is the adjacent side
the sloping longest side is the hypotenuse
the bottom horizontal side across from $θ\theta$ is the opposite side

Trigonometric Ratios Lesson

Trigonometric Ratios Lesson