MCQ 511 Mark
$\cos 60^{\circ} \cos 30^{\circ}-\sin 60^{\circ} \sec 30^{\circ}=$ ?
- ✓$\cos 90^{\circ}$
- B$\sin 90^{\circ}$
- C$\sin 45^{\circ}$
- D$\cos 45^{\circ}$
Answer
View full question & answer→Correct option: A.
$\cos 90^{\circ}$
$\cos 60^{\circ} \cos 30^{\circ}-\sin 60^{\circ} \sin 30^{\circ}$
$=\frac{1}{2} \times \frac{\sqrt{3}}{2}-\frac{\sqrt{3}}{2} \times \frac{1}{2}$
$=\frac{\sqrt{3}}{4}-\frac{\sqrt{3}}{4}=0$
$=\cos 90^{\circ}$
$=\frac{1}{2} \times \frac{\sqrt{3}}{2}-\frac{\sqrt{3}}{2} \times \frac{1}{2}$
$=\frac{\sqrt{3}}{4}-\frac{\sqrt{3}}{4}=0$
$=\cos 90^{\circ}$
