Tìm x biết : a) \(x - {1 \over 3} = - {1 \over 2}\) ; b) \( - {2 \over 5} - x = - {3 \over 8}\);
c) \( - {2 \over 3}x - 5 = 7\).
\(\eqalign{ & a) \cr & x - {1 \over 3} = - {1 \over 2} \cr & x = - {1 \over 2} + {1 \over 3} \cr & x = - {3 \over 6} + {2 \over 6} \cr & x = {{ - 1} \over 6} \cr} \) \(\eqalign{ & b) \cr & - {2 \over 5} - x = - {3 \over 8} \cr & - x = {{ - 3} \over 8} + {2 \over 5} \cr & - x = {{ - 15} \over {40}} + {{16} \over {40}} \cr & - x = {1 \over {40}} \cr & x = {{ - 1} \over {40}} \cr} \) \(\eqalign{ & c) \cr & - {2 \over 3}x - 5 = 7 \cr & - {2 \over 3}x = 7 + 5 = 12 \cr & x = 12.{3 \over { - 2}} \cr & x = - 18 \cr} \)