Question

Evaluate Cos^-1(sin 330 degree)

Answer 1

`330^\circ\equiv-30^\circ\mod360^\circ`

so


`\sin330^\circ=\sin(-30^\circ)=-\sin30^\circ=-\frac12`

Finally,


`\cos^(-1)\left(-\frac12\right)=\frac{2\pi}3\text{ rad}=120^\circ`