Rander Lim Boon Chun's answer to Lucas loke's Secondary 4 E Maths question.

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Rander Lim Boon Chun
Rander Lim Boon Chun's answer
26 answers (Tutor Details)
Use cosine rule. Not that its ok for the value to be negative since the angle is obtuse ( more than 90 but less than 180)