SPM 2019 Add Maths Paper 1, Question 12Circular Measure

Solved on video in English and Bahasa Melayu · 3 marks · Form 5, Circular Measure · 3:55 video

The question

Diagram 4 shows a rhombus OACB inscribed in sector AOB with centre O and radius r cm, where angle AOB = alpha rad. Given the area of sector AOB is 18 cm², express (a) alpha in terms of r, (b) the perimeter, in cm, of the shaded region in terms of r.

[3 marks]

SPM 2019 Add Maths Paper 1, Question 12: the question as drawn in Eduly's video3:55

Step 1

Area of sector AOB = (1/2) r² alpha = 18, so alpha = 36/r².

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

Final answer

(a) α = 36/r²; (b) Perimeter = 2r + 36/r cm

Where students lose marks

Watch out: all rhombus sides equal r, so AC = CB = r. Do not add the straight line AB to the shaded perimeter.

Watch every step of this question solved on video (3:55), with the reason behind each step and a box that checks your own answer.

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