I'm in physics I and only in Trig for the first time this year (Jr in HS). I do not remember sin (2 theta) in any previous lessons. I need in help in the following problem using it. In a double-slit experiment with monochromatic light and a screen at a distance of 1.50 , the angle between the second-order bright fringe and the central maximum is 0.0230 rad. If the seperation distance of the slits is 0.0350 mm, what are (a) the wavelength and color of the light and (b) the lateral displacement of the fringe. I am so confused with the question. I'm not even sure i need the sin (2 theta) in here. Any help will be appreciated. I am new to the site (found in a google search). So if this is the wrong forum, I appologize.