Question

Please help!!!! the question is in screenshot

Answer 1

Answer:

$-\cos nw_0t$

Step-by-step explanation:

We can use the double angle identity for sine.

$\sin (A+B)=\sin A \cos B+\sin B\cos A$

The given expresion is

$\sin (nw_0t-90)$

We apply the identity to get:

$\sin (nw_0t-90)=\sin nw_0t \cos 90-\cos nw_0t \sin 90$

We simplify to obtain;

$\sin (nw_0t-90)=\sin nw_0t (0)-\cos nw_0t (1)$

This simplifies to:

$\sin (nw_0t-90)=-\cos nw_0t$ The correct answer is D