Wiskunde Multiple Choice Vraag uit Gricha's Wiskundige Vragenbank

sin 285° + cos 75° =	A. −
B.
C. −
D.
E. −

$\sin 285^{\circ} + \cos 75^{\circ}\\=\cos 75^{\circ} - \sin 105^{\circ}\\=\sin 15^{\circ} - \sin 105^{\circ}\\=\cos \frac{15^{\circ}+105^{\circ}}{2}.\sin \frac{15^{\circ}-105^{\circ}}{2}\\=2.\cos 60^\circ.\sin(-45^\circ)\\=-2.\frac 12.\frac{\sqrt{2}}{2} \\=-\frac{\sqrt{2}}{2}$