cos(300) is equal to sin(?)

and

sin(150)=sin(30)

I would have said

cos(300)=cos(360-300)=cos(60)=sin(30)

cos (300) = 0.5      Sin (x) = 0.5    x= Sin-1 (0.5) =  30 degrees

cos(300) is equal to sin(?)

$$\small{ \cos{(300\ensurement{^{\circ}})} \text{ is equal to } \sin{(90\ensurement{^{\circ}}-300\ensurement{^{\circ}} )} = \sin{(-210\ensurement{^{\circ}} )} = \sin{(-210\ensurement{^{\circ}} + 360 \ensurement{^{\circ}} )} =\sin{(150 \ensurement{^{\circ}} } )} }$$