486.
$$\eqalign{
\frac{{a - 1}}{{{a^2}}} \cdot \frac{{ax - a}}{{a - 1}} + \frac{{1 - x}}{{2a}}
} $$
487.
$$\eqalign{
\frac{{{x^2} - xy}}{{y - 1}} \cdot \frac{{y - 1}}{{{x^2}}} + \frac{{y - x}}{{2x}}
} $$
488.
$$\eqalign{
\frac{x}{a} - \frac{{{x^2} - {a^2}}}{{{a^2}}} \cdot \frac{a}{{x + a}}
} $$
489.
$$\eqalign{
b - \frac{{2a}}{{a - b}} \cdot \frac{{{a^2} - {b^2}}}{{4a}}
} $$
490.
$$\eqalign{
a - \frac{{{a^2} - 5a}}{{a + 1}} \cdot \frac{1}{{a - 5}}
} $$
494.
$$\eqalign{
\left( {\frac{{4x}}{{x + 2}} + 2x} \right) \cdot \frac{{x + 2}}{{4{x^2}}}
} $$
498.
$$\eqalign{
\left( {a + 4} \right) \cdot \frac{{a + 6}}{{{a^2} - 16}} - \frac{{a - 6}}{{a - 4}}
} $$
500.
$$\eqalign{
\frac{{y - xy}}{3} \cdot \frac{6}{{1 - {x^2}}} - \frac{y}{{1 + x}}
} $$
514.
$$\eqalign{
\frac{{3a}}{{1 + c}} - \frac{4}{{1 - {c^2}}} \cdot \frac{{a - ac}}{2}
} $$
515.
$$\eqalign{
2c \cdot \frac{c}{{{a^2} - {c^2}}}:\frac{{{c^2}}}{{{a^2} + ac}}
} $$
516.
$$\eqalign{
bc:\frac{{{b^2} - {c^2}}}{{3c}} \cdot \frac{{b - c}}{{{c^2}}}
} $$
517.
$$\eqalign{
\frac{{{x^2} - {y^2}}}{{xy}}:\frac{{x - y}}{{3y}} \cdot \frac{1}{{x + y}}
} $$