Physics - Calculus Question with Solution | TestHub

The angle $\pi /2$ radians is equivalent to $90^{\circ }$.

The cosine function represents the x-coordinate of a point on the unit circle corresponding to the given angle.

For an angle of $90^{\circ }$ (or $\pi /2$ radians), the point on the unit circle is $(0,1)$. The x-coordinate is 0. Therefore, $\cos (\pi /2)=0$.