| Exam Board | Edexcel |
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| Module | AS Paper 1 (AS Paper 1) |
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| Topic | Sine and Cosine Rules |
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7. In a triangle \(P Q R , P Q = 20 \mathrm {~cm} , P R = 10 \mathrm {~cm}\) and angle \(Q P R = \theta\), where \(\theta\) is measured in degrees. The area of triangle \(P Q R\) is \(80 \mathrm {~cm} ^ { 2 }\).
a. Show that the two possible values of \(\cos \theta = \pm \frac { 3 } { 5 }\)
Given that \(Q R\) is the longest side of the triangle,
b. find the exact perimeter of the triangle \(P Q R\), giving your answer as a simplified surd.