November 2021 Paper 1 Q18
18 Here is a triangle.
Not drawn accurately
Use the cosine rule to work out the value of \(x\). [4 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(7^2 = x^2 + 3^2 - 2 \times 3 \times x \cos 60^\circ\) | M1 | oe |
| \(x^2 - 3x - 40\ (= 0)\) | A1 | |
| \((x - 8)(x + 5)\ (= 0)\) or \(\dfrac{--3 \pm \sqrt{(-3)^2 - 4 \times 1 \times -40}}{2 \times 1}\) | M1 | oe follow through their three term quadratic |
| 8 | A1 |
Additional guidance
If \(-5\) is also given as an answer then do not award final A mark