Interference pattern is formed on a screen by Young’s double slits S1 and S2 which are identical and illuminated by monochromatic light of wavelength  λ . Points P and P´ are on the screen closest to and on either side of central maxima, where intensity is one fourth of  that at the central maxima. If PP'=2Dλdx.  Find x.(assume d>>λ&D>>d )