## Trigonometry 7th Edition

One complete revolution is equivalent to $360^{\circ}$ Time taken to rotate through $360^{\circ}$ = 4 seconds Time taken to rotate through $1^{\circ}$ = $\frac{4}{360}$ seconds Time taken to rotate through $90^{\circ}$ = $\frac{4}{360} \times 90$ seconds = 1 second