How wide is the base of a trihedral prism which has the same resolving power as a diffraction grating with 10000 lines in the second order of the spectrum if ∣d⃗∣/dλ∣=0.10μm−1?|\vec{d}| / d \lambda \mid=0.10 \mu \mathrm{m}^{-1} ?∣d∣/dλ∣=0.10μm−1?