Single Slit Exp: Find Number of Minima in 0-19deg Range

[dsptl]

A single slit with width 819 nm is illuminated with light of wavelength 405 nm. How many
minima occur in the angular range from theta = 0 to theta = ±19deg?


I have an exam tomm please help me out with some problems.

actually, i hv the answer but i don't know how to derive it!

 

[tamz273]

i just googled 4 keywords and got the formula, try it! :)

 

[dsptl]

Please Help me though!

 

[Carid]

tan(theta) = m * Wavelength/SlitWidth

You know all the values except m.
m is the number of minima (it's an integer obviously).

Be careful about the angle, its a plus-minus.