How Do You Calculate the Third Maximum for a Single Slit Diffraction?

[wilson_chem90]

A single slit is illuminated with a helium-neon laser whose wavelength is 633 nm. If the slit width is 2.2 x 10^-5 m, calculate the third maximum in degrees.

Relevant equations:
sinO = (m + 1/2)x(wavelength) / w

The attempt at a solution:
sinO = (m + 1/2)x(wavelength) / w

sinO = (3 + 1/2)x(633 x 10^-9 m) / (2.2 x 10^-5 m)
O = sin inverse0.100704545 m
O = 5.8 degrees

The third maximum is approx. 6 degrees.

Im not completely sure if this is correct.

 

[willem2]

It's correct. sinO = (m + 1/2)x(wavelength) / w is only approximate anyway. only
the minima can be calculated exactly with sinO = (m)x(wavelength) / w