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
\[\eqalign{ & a]178 - 3x = 25 \cr & 3x = 178 - 25 \cr & 3x = 153 \cr & x = 153:3 \cr & x = 51 \cr & b]\left[ {x + 67} \right] - 28 = 49 \cr & x + 67 = 49 + 28 \cr & x + 67 = 77 \cr & x = 77 - 67 \cr & x = 10 \cr & c]160:\left[ {x - 15} \right] = 8 \cr & x - 15 = 160:8 \cr & x - 15 = 20 \cr & x = 20 + 15 \cr & x = 35 \cr & d]189 - 2.\left[ {93 - x} \right] = 25 \cr & 2.[93 - x] = 189 - 25 \cr & 2.[93 - x] = 164 \cr & 93 - x = 164:2 \cr & 93 - x = 82 \cr & x = 93 - 82 \cr & x = 11 \cr & e]15x - 57 = {3^2}{.3^3} \cr & 15x - 57 = 9.27 \cr & 15x - 57 = 243 \cr & 15x = 243 + 57 \cr & 15x = 300 \cr & x = 300:15 \Leftrightarrow x = 20 \cr & g]\left[ {\left[ {6x - 39} \right]:3} \right].28 = 5628 \cr & [6x - 39]:3 = 5628:28 \cr & [6x - 39]:3 = 201 \cr & 6x - 39 = 201.3 \cr & 6x - 39 = 603 \cr & 6x = 603 + 39 \cr & 6x = 642 \cr & x = 642:6 \Leftrightarrow x = 107 \cr} \]