\(a,\dfrac{1}{2}=\dfrac{1}{3}+\dfrac{1}{6}\\ \dfrac{1}{3}=\dfrac{1}{4}+\dfrac{1}{12}\\ b,\dfrac{1}{2}=\dfrac{1}{12}+\dfrac{1}{4}+\dfrac{1}{6};\dfrac{1}{3}=\dfrac{1}{24}+\dfrac{1}{8}+\dfrac{1}{6}\\ c,\dfrac{1}{2}=\dfrac{1}{24}+\dfrac{1}{12}+\dfrac{1}{8}+\dfrac{1}{4};\dfrac{1}{3}=\dfrac{1}{48}+\dfrac{1}{12}+\dfrac{1}{16}+\dfrac{1}{6}\\ d,\dfrac{1}{2}=\dfrac{1}{1}-\dfrac{1}{2};\dfrac{1}{3}=\dfrac{1}{2}-\dfrac{1}{6}\)