Đề bài
Tìm số tự nhiên x, biết :
\(\eqalign{ & a)\;178 - 3x = 25 \cr & b)\;\left( {x + 67} \right) - 28 = 49 \cr & c)\;160:\left( {x - 15} \right) = 8 \cr & d)\;189 - 2.\left( {93 - x} \right) = 25 \cr & e)\;15x - 57 = {3^2}{.3^3} \cr & g)\;\left[ {\left( {6x - 39} \right):3} \right].28 = 5628. \cr} \)
Lời giải chi tiết
\(\eqalign{ & a)178 - 3x = 25 \cr & 3x = 178 - 25 \cr & 3x = 153 \cr & x = 153:3 \cr & x = 51 \cr & b)\left( {x + 67} \right) - 28 = 49 \cr & x + 67 = 49 + 28 \cr & x + 67 = 77 \cr & x = 77 - 67 \cr & x = 10 \cr & c)160:\left( {x - 15} \right) = 8 \cr & x - 15 = 160:8 \cr & x - 15 = 20 \cr & x = 20 + 15 \cr & x = 35 \cr & d)189 - 2.\left( {93 - x} \right) = 25 \cr & 2.(93 - x) = 189 - 25 \cr & 2.(93 - x) = 164 \cr & 93 - x = 164:2 \cr & 93 - x = 82 \cr & x = 93 - 82 \cr & x = 11 \cr & e)15x - 57 = {3^2}{.3^3} \cr & 15x - 57 = 9.27 \cr & 15x - 57 = 243 \cr & 15x = 243 + 57 \cr & 15x = 300 \cr & x = 300:15 \Leftrightarrow x = 20 \cr & g)\left[ {\left( {6x - 39} \right):3} \right].28 = 5628 \cr & (6x - 39):3 = 5628:28 \cr & (6x - 39):3 = 201 \cr & 6x - 39 = 201.3 \cr & 6x - 39 = 603 \cr & 6x = 603 + 39 \cr & 6x = 642 \cr & x = 642:6 \Leftrightarrow x = 107 \cr} \)
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