B) c(c+3) 3d d c n² m-n г) m(m+n) 3m

в) $$\frac{3d}{c(c+3)} - \frac{d}{c} = \frac{3d - d(c+3)}{c(c+3)} = \frac{3d - cd - 3d}{c(c+3)} = \frac{-cd}{c(c+3)} = \frac{-d}{c+3}$$ г) $$\frac{n^2}{m(m+n)} - \frac{m-n}{3m} = \frac{3n^2 - (m-n)(m+n)}{3m(m+n)} = \frac{3n^2 - (m^2 - n^2)}{3m(m+n)} = \frac{3n^2 - m^2 + n^2}{3m(m+n)} = \frac{4n^2 - m^2}{3m(m+n)}$$ Ответ: в) $$\frac{-d}{c+3}$$; г) $$\frac{4n^2 - m^2}{3m(m+n)}$$