MRSM Trial 2025 Add Maths Paper 1, Question 4Trigonometric Functions

Solved on video in English · Form 5, Trigonometric Functions · 3:36 video

The question

It is given that sin(90° − β) = h, such that β is an acute angle. Express cosec β in terms of h.

Step 1

Use the complementary-angle identity: sin(90° − β) = cos β, so cos β = h.

Why this step

The angle 90° − β is the other angle in the triangle, so its sine equals cos β. Writing sin β here is the classic mistake.

2 more steps, each with the reason for it, in the full solution

Final answer

cosec β = 1/√(1 − h²)

Where students lose marks

Watch out: sin(90° − β) = cos β, not sin β. Take the positive root of √(1 − h²) since β is acute.

Watch every step of this question solved on video (3:36), with the reason behind each step and a box that checks your own answer.

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