Trigonometry — O/L Mathematics

What must I remember about Trigonometry?

• Trigonometric ratios in a right-angled triangle relative to acute angle θ: Sine (sin θ) = Opposite / Hypotenuse.
• Cosine (cos θ) = Adjacent / Hypotenuse; Tangent (tan θ) = Opposite / Adjacent = sin θ / cos θ.
• Angle of elevation: The angle formed between the horizontal line of sight and the observer's line of sight looking UPWARDS at an elevated object.
• Angle of depression: The angle formed between the horizontal line of sight and the observer's line of sight looking DOWNWARDS at an object.
• Equality of alternate angles: Angle of depression from point A to point B equals the angle of elevation from point B to point A.

Test yourself (1 minute)

1. Angle of depression baseline trap

   The angle of depression is measured from the HORIZONTAL line of sight, NEVER from the vertical cliff or mast.

2. Observer height addition

   If an observer of height h stands on ground looking at a building of height H, the opposite side is (H - h); remember to add h back when calculating total height.

3. Trigonometric table lookups

   In Paper 2 trigonometry problems, show the ratio substitution clearly before writing the four-figure table decimal reading.

Practise Trigonometry questions today

Source: NIE G.C.E. (O/L) Mathematics Syllabus (Grade 11, Unit 18)

What comes next?

Next in the syllabus

Where does Trigonometry fit in the syllabus?

Grade 11 · Term 3