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

(a)

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.

(b)

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'.

SPM 2021 Add Maths Paper 2, Question 14: the question as drawn in Eduly's video7:49

Part (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.

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

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