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)

$1$

Answer 2

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