Tìm giá trị x biết: (dfrac{x}{126}=dfrac{-5}{9}.dfrac{4}{7})

Ta có:

 (eqalign{ & {x over {126}} = {{ – 5} over 9}.{4 over 7} cr & {x over {126}} = {{ (- 5).4} over 9.7}cr & {x over {126}} = {{ – 20} over {63}} cr & {x over {126}} = {{ – 40} over {126}} cr & ,,,,,,x = – 40 cr})