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SPM Additional Mathematics 2019, Paper 2 (Question 13)


Question 13:
Solution by scale drawing is not accepted.
Diagram 6 shows a quadrilateral ABCD such that AC and BD are straight lines.

Diagram 6

It is given that the area of ∆
ABC = 6 cm2 and ABC is obtuse.
(a) Find
(i) ABC,
(ii) the length, in cm, of AC,
(iii) BAC            [7 marks]
(b) Given BD = 7.3 cm and BCD = 90°, calculate the area in cm2, of ∆ACD. [3 marks]


Solution:
(a)(i)
Area of Δ ABC=6 cm212×4×3.5×sinABC=6ABC=121o

(a)(ii)
AC2=42+3.522(4)(3.5)cos121oAC=6.532 cm

(a)(iii)
sinBAC3.5=sin1216.532sinBAC=3.5×sin1216.532BAC=27o20

(b)
cosCBD=3.57.3CBD=61o21ABD=121o61o21          =59o39Area of ΔACD=Area of ΔCBD+Area of ΔABD6=(12×3.5×7.3×sin61o21)+(12×4×7.3×sin59o39)6=18.434 cm26=12.434 cm2

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