#theta# is the angle between the diffracted ray and normal to the grating, and
#d# being the distance from the center of one slit to the center of the adjacent slit.
Condition for constructive interference, maximum, is the distance #bc# be integral multiple of wavelength #lambda#.
In #Delta abc, angle bac=theta#, from geometry.
#:. "distance " bc=d.sintheta#
Grating formula becomes
#d.sintheta_m=mlambda#, where #m# is integer representing the maximum of interest.
In the problem, it is first order maxima #m=1#
Therefore the expression becomes
#d.sintheta_1=1.lambda=lambda#, inserting the given quantities
Wavelength #lambda=1.00xx10^-6cdot sin 70.0^@#
#=1.00xx10^-6cdot 0.93969#
#=9.3969xx10^-7 m#
