Question

The value of $Cos(270^{\circ }+\theta )Cos(90^{\circ }-\theta )-Sin(270^{\circ }-\theta )Cos\theta$ is

• A. $0$
• B. $-1$
• C. $\frac{1}{2}$
• D. $1$

Answer 1

Answer: (D)

$\cos \left(270^{\circ }+\theta \right)\cos \left(90^{\circ }-\theta \right)$
$-\sin \left(270^{\circ }-\theta \right)\cos \theta$
$=\sin \theta \cdot \sin \theta +\cos \theta \cdot \cos \theta$
$={\sin }^2\theta +{\cos }^2\theta =1$