A wave has a frequency of 775 Hz. What is its period?

The period is simply the inverse of the frequency, therefore:

T = 1 / f

T = 1 / 775 Hz

T = 0.001290 s    → possible answer

T = 1.29 × 10⁻³ s   → possible answer

T = 1.29 ms          → possible answer

what is the question?

the working equation for the angular size is the product of the physical size and 360 degrees divided by the product of two pi and distance from earth. the minimum size would be 0.559 degrees while the maximum size would be 0.49 degrees.