\[\eqalign{ & a] \cr & x - {1 \over 3} = - {1 \over 2} \cr & x = - {1 \over 2} + {1 \over 3} \cr & x = - {3 \over 6} + {2 \over 6} \cr & x = {{ - 1} \over 6} \cr} \] \[\eqalign{ & b] \cr & - {2 \over 5} - x = - {3 \over 8} \cr & - x = {{ - 3} \over 8} + {2 \over 5} \cr & - x = {{ - 15} \over {40}} + {{16} \over {40}} \cr & - x = {1 \over {40}} \cr & x = {{ - 1} \over {40}} \cr} \] \[\eqalign{ & c] \cr & - {2 \over 3}x - 5 = 7 \cr & - {2 \over 3}x = 7 + 5 = 12 \cr & x = 12.{3 \over { - 2}} \cr & x = - 18 \cr} \]
Đề bài
Tìm x biết : a] \[x - {1 \over 3} = - {1 \over 2}\] ; b] \[ - {2 \over 5} - x = - {3 \over 8}\];
c] \[ - {2 \over 3}x - 5 = 7\].
Lời giải chi tiết
\[\eqalign{ & a] \cr & x - {1 \over 3} = - {1 \over 2} \cr & x = - {1 \over 2} + {1 \over 3} \cr & x = - {3 \over 6} + {2 \over 6} \cr & x = {{ - 1} \over 6} \cr} \] \[\eqalign{ & b] \cr & - {2 \over 5} - x = - {3 \over 8} \cr & - x = {{ - 3} \over 8} + {2 \over 5} \cr & - x = {{ - 15} \over {40}} + {{16} \over {40}} \cr & - x = {1 \over {40}} \cr & x = {{ - 1} \over {40}} \cr} \] \[\eqalign{ & c] \cr & - {2 \over 3}x - 5 = 7 \cr & - {2 \over 3}x = 7 + 5 = 12 \cr & x = 12.{3 \over { - 2}} \cr & x = - 18 \cr} \]