Selangor Trial 2025 Add Maths Paper 1, Question 1Circular Measure

Solved on video in English · Form 5, Circular Measure · 3:47 video

The question

Diagram 1 shows an arc PQ which subtends an angle of 1.2 rad at the centre O of the circle. The radius of the circle is 8 cm.

Find the area, in cm², of the shaded region and give the answer correct to four significant figures. [Use π = 3.142]

Step 1

The shaded region is the major sector, i.e. the whole circle minus the 1.2 rad minor sector. Its angle is the reflex angle at O: θ = 2π − 1.2.

Why this step

The shaded part is the rest of the full turn, so we use the reflex angle 2π − 1.2. Using 1.2 would give the unshaded wedge instead.

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

Final answer

162.7 cm²

Where students lose marks

Watch out: the shaded part is the major sector, so use the reflex angle 2π − 1.2, not 1.2, and round to 4 s.f.

Watch every step of this question solved on video (3:47), with the reason behind each step and a box that checks your own answer.

No card. Every past-year question on video, in English and BM.