Bài 71 trang 37 SGK Toán 6 tập 2

Tìm x, biết:

a) \(x-\dfrac{1}{4}=\dfrac{5}{8}.\dfrac{2}{3}\) ;              b) \(\dfrac{x}{126}=\dfrac{-5}{9}.\dfrac{4}{7}\) ;

a) 

\(\eqalign{
& x - {1 \over 4} = {5 \over 8}.{2 \over 3} \cr
& x - {1 \over 4} = {5 \over {12}} \cr
& x\,\,\,\,\,\,\,\,\,\, = {5 \over {12}} + {1 \over 4} \cr
& x\,\,\,\,\,\,\,\,\,\, = {8 \over {12}} = {2 \over 3} \cr} \)

b) 

\(\eqalign{
& {x \over {126}} = {{ - 5} \over 9}.{4 \over 7} \cr
& {x \over {126}} = {{ - 20} \over {63}} \cr
& 63.x = - 20.126 \cr
& \,\,\,\,\,\,x = {{ - 20.126} \over {63}} \cr
& \,\,\,\,\,\,x = - 40 \cr} \)