Đáp án:
a, x + $\frac{1}{5}$ = $\frac{3}{7}$
⇔ x = $\frac{3}{7}$ - $\frac{1}{5}$
⇔ x =$\frac{15}{35}$ - $\frac{7}{35}$
⇔ x = $\frac{8}{35}$
b, x- $\frac{3}{4}$ = $\frac{1}{2}$
⇔ x = $\frac{1}{2}$ + $\frac{3}{4}$
⇔ x = $\frac{5}{4}$
c, - x - $\frac{9}{2004}$ = $\frac{-1}{2003}$
⇔ - x = $\frac{-1}{2003}$ + $\frac{9}{2004}$
⇔ - x = $\frac{16023}{4014012}$
⇔ x = $\frac{-16023}{4014012}$
d, $\frac{5}{9}$ - x = $\frac{1}{2004}$
⇔ x = $\frac{5}{9}$ - $\frac{1}{2004}$
⇔ x = $\frac{3337}{6012}$
