SPM 2021 Add Maths Paper 2, Question 14Solution of Triangles
Solved on video in English and Bahasa Melayu · Form 4, Solution of Triangles · 7:49 video
The question
Solution by scale drawing is not accepted. Diagram 6 shows a quadrilateral ABCD. Point E is the intersection point of the straight lines AC and BD. It is given that AB = 2.8 cm, BC = 3 cm, DC = 3.6 cm, the area of triangle ABC is equal to the area of triangle BCD, AE = 4 cm, angle ABC = 143° and angle BCD is an obtuse angle. (a) Calculate (i) angle BCD, (ii) the length, in cm, of CE, (iii) the length, in cm, of BE.
From part (a), triangle ABC has AC = 5.501 cm, BC = 3 cm, angle BAC = 19.16° and angle ABC = 143°. (b)(i) Sketch a triangle A'B'C' which has a different shape from triangle ABC such that A'C' = AC, B'C' = BC and angle B'A'C' = angle BAC. (b)(ii) Hence, state the size of angle A'B'C'.
7:49Part (a)
Step 1
Area of triangle ABC = (1/2)(AB)(BC) sin(ABC) = (1/2)(2.8)(3) sin 143° = 4.2 × 0.6018 = 2.5276 cm².
11 more steps, each with the reason for it, in the full solution
Final answer
angle BCD = 152.09°, CE = 1.501 cm, BE = 1.637 cm
Where students lose marks
Watch out: an obtuse angle is 180° minus the reference angle, not plus. Also take the square root of BE² at the end.
Part (b)
3 more steps, each with the reason for it, in the full solution
Final answer
Sketch (see video); angle A'B'C' = 37°
Where students lose marks
Watch out: give the size of angle A'B'C' (37°), not just its type such as 'obtuse'.
Watch every step of this question solved on video (7:49), with the reason behind each step and a box that checks your own answer.
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