In diffraction due to a single slit, what is the condition for first minimum ?

Discuss diffraction at single slit and obtain the consition for n^(th) minimum. Diffraction at single slit:

In a diffraction pattern due to a single slit of width a, the first minimum is observed at an angle 30^(@) when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observed at an angle of ...

In a diffraction pattern due to a single slit of width a, the first minimum is observed at an angle 30^(@) when light of wavelength 5000Å is incident on the slit. The first secondary maximum is observed at an angle of

In a diffraction pattern due to a single slit of width 'a' the first minimum is obsrved at an angle 30^@ When light of wavelength 5000 overset@A is incident on the slit.The first secondary maximum is oberved at an angle of :