June 2019 Paper 1 Q15
15 Here is a sketch graph of \(\quad y = \cos x \quad\) for \(\quad 0^\circ \leqslant x \leqslant 360^\circ\)
You are given that \(\quad \cos 36^\circ = 0.8090\)
Solve \(\quad \cos x = -0.8090 \quad\) for \(\quad 0^\circ \leqslant x \leqslant 360^\circ\) [2 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(144^\circ\) | B1 | answers should be on answer line but can be accepted if they are the only angles written on the diagram (other than \(36^\circ\) which is the question so fine) condone missing degree sign |
| \(216^\circ\) | B1 |
Additional guidance
| Don’t accept \(\cos 144^\circ\), \(\cos 216^\circ\), \(\cos x = 144^\circ\), \(\cos x = 216^\circ\) | B0 |
| Accept \(\cos 144^\circ = -0.8090\) and \(\cos 216^\circ = -0.8090\) | B1, B1 |
| If more than 2 angles offered this is choice 4 or more angles 2 wrong 1 right 1 wrong 2 right 1 wrong 1 right | B0 B0 B1 B1 |