Trả lời câu hỏi 2 Bài 2 trang 9 SGK Toán 7 Tập 1

Đề bài

Tìm $x$, biết:

$\eqalign{ & a)\,\,x - {1 \over 2} = - {2 \over 3} \cr & b)\,\,{2 \over 7} - x = - {3 \over 4} \cr}$ 

Lời giải chi tiết

$\eqalign{ & a)\,\,x - {1 \over 2} = - {2 \over 3} \cr & \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\, = - {2 \over 3} + {1 \over 2} \cr & \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\, =  {-2.2 \over 3.2} + {1.3 \over 2.3} \cr  & \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\, = {{ - 4} \over 6} + {3 \over 6} \cr & \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\, = {{ - 4+3} \over 6} \cr & \,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\, = {{ - 1} \over 6} \cr & b\,)\,\,{2 \over 7} - x = - {3 \over 4} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {2 \over 7} - \left( { - {3 \over 4}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {2 \over 7} + {3 \over 4} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {2.4 \over 7.4} + {3.7 \over 4.7} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {8 \over {28}} + {{21} \over {28}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {8+21 \over {28}} \cr  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x = {{29} \over {28}} \cr}$

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