Упростите выражения:

$a) \frac{ m^{2} + n^{2} }{ m^{3} + n^{3} } - \frac{1}{2(m+n)} = \frac{ m^{2} + n^{2} }{(m+n)(m^{2}-mn+n^{2})} - \frac{1}{2(m+n)}$ $= \frac{2(m^{2}+n^{2})-(m^{2}-mn+n^{2})}{2(m+n)(m^{2}+mn+n^{2})} = \frac{m^{2}+mn+n^{2}}{2(m+n)(m^{2}-mn+n^{2})}$

(p-q)(p^{2}+pq+q^{2})(p+q)}" alt="b) \frac{2(p+q)}{p^{3}-q^{3}} + \frac{2}{q^{2}-p^{2}} = \frac{(p+q)(2p+2q)-(p^{2}+pq+q^{2})2}{(p-q)(p^{2}+pq+q^{2})(p+q)} = \frac{2p^{2}+4pq+2q^{2}-2p^{2}-2pq-2q^{2}}{(p-q)(p^{2}+pq+q^{2})(p+q)}" align="absmiddle" class="latex-formula"> $= \frac{2pq}{(p-q)(p^{2}+pq+q^{2})(p+q)}$