We are given the property of the illuminating light:
790 lines/mm
Which is also equivalent to:
790,000 lines/m
Taking the reciprocal of this value will give us the distance per line:
d = 1 m / 790,000 lines
d = 1.2658 * 10^-6 m
Now we can solve for the range of angles using the formula
λ = d * sin θ
sin θ = λ / d
where λ is the wavelength of light and θ is the angle
Now we know that visible light ranges from 400 to 700 nm, therefore we use these values to find the range.
when λ = 400 nm = 400 * 10^-9 m
sin θ = 400 * 10^-9 m / 1.2658 * 10^-6 m
θ = 18.42°
when λ = 700 nm = 700 * 10^-9 m
sin θ = 700 * 10^-9 m / 1.2658 * 10^-6 m
θ = 33.57°
Therefore the range of angles is 18.42° to 33.57°.